Washington and its western allies have for the first time since the end of the cold war drawn up classified military plans to defend the most vulnerable parts of eastern Europe against Russian threats, according to confidential US diplomatic cables.

The US state department ordered an information blackout when the decision was taken earlier this year. Since January the blueprint has been refined.

Nine Nato divisions – US, British, German, and Polish – have been identified for combat operations in the event of armed aggression against Poland or the three Baltic states. North Polish and German ports have been listed for the receipt of naval assault forces and British and US warships. The first Nato exercises under the plan are to take place in the Baltic next year, according to informed sources.

Following years of transatlantic dispute over the new policy, Nato leaders are understood to have quietly endorsed the strategy at a summit in Lisbon last month.

Despite President Barack Obama's policy of "resetting" relations with Russia, which was boosted at the Nato summit attended by Russian president, Dmitry Medvedev, the state department fears that the major policy shift could trigger "unnecessary tensions" with Moscow.

The decision to draft contingency plans for Estonia, Latvia and Lithuania was taken secretly earlier this year at the urging of the US and Germany at Nato headquarters in Belgium, ending years of division at the heart of the western alliance over how to view Vladimir Putin's Russia.

The decision, according to a secret cable signed by Hillary Clinton, the US secretary of state, marks the start of a major revamp of Nato defence planning in Europe.

The strategy has not been made public, in line with Nato's customary refusal to divulge details of its "contingency planning" – blueprints for the defence of a Nato member state by the alliance as a whole.

These are believed to be held in safes at Nato's planning headquarters in Mons, Belgium.

According to a secret cable from the US mission to Nato in Brussels, US admiral James Stavridis, the alliance's top commander in Europe, proposed drawing up defence plans for the former Soviet Baltic states of Lithuania, Latvia, and Estonia.

The policy was put to top military officials from Nato's 28 states. "On January 22 Nato's military committee agreed … under a silence procedure", the cable notes, referring to a decision carried by consensus unless someone speaks up to object.

Attempts by Stavridis's predecessor, General John Craddock, to push through defence planning for the Baltic were stymied by German-led opposition in western Europe, anxious to avoid upsetting the Kremlin.The policy shift was decided by senior military officials rather than Nato's top decision-taking body, the North Atlantic Council, in order to avoid repeating the splits and disputes on the issue over the past five years. The plan entails grouping the Baltic states with Poland in a new regional defence scheme that has been worked on in recent months and is codenamed Eagle Guardian.

In parallel negotiations with Warsaw the US has also offered to beef up Polish security against Russia by deploying special naval forces to the Baltic ports of Gdansk and Gdynia, putting squadrons of F-16 fighter aircraft in Poland and rotating C-130 Hercules transport planes into Poland from US bases in Germany, according to the diplomatic cables, almost always classified secret.

Earlier this year the US started rotating US army Patriot missiles into Poland in a move that Warsaw celebrates publicly as boosting Polish air defences and demonstrating American commitment to Poland's security.

But the secret cables expose the Patriots' value as purely symbolic. The Patriot battery, deployed on a rotating basis at Morag in north-eastern Poland, 40 miles from the border with Russia's Kaliningrad exclave, is purely for training purposes, and is neither operational nor armed with missiles.

At one point Poland's then deputy defence minister privately complained bitterly that the Americans may as well supply "potted plants'.

Since joining Nato in 2004, the three Baltic states have complained they are treated as second-class members because their pleas for detailed defence planning under Nato's "all for one and one for all" article 5 have been being ignored. Article 5 is the heart of Nato's founding treaty, stipulating that the alliance will come to the rescue of any member state attacked. The only time it has been invoked was following 9/11 when the European allies and Canada rallied to support America.

The Poles and the Baltic states have long argued that rhetorical declarations of commitment to article 5 are meaningless without concrete defence planning to back them up.

The Baltic demands for hard security guarantees became much more desperate in the past three years.

A cyber-attack on Estonia in 2007 was believed to have originated in Russia, and the Kremlin invaded Georgia a year later.

Nerves were further set on edge last year when the Russians staged exercises simulating an invasion of the Baltic states and a nuclear attack on Poland.

The eastern European calls for hard security guarantees, however, were stymied by western Europe, led by Germany, which did not want to antagonise Russia.

"We've found the way forward with Russia. The Baltic states have received strategic reassurance," said a well-placed source. "That's backed up with contingency planning that did not exist before. It's done now. We told them we'll give you your reassurance if you agree to the reset with Russia. That made it easier for the Germans."During intense – if discreet – diplomacy last year, the resistance was overcome by the Americans, and the new policy was tabled as a joint US-German move.

"Most of the information on this is not in the public domain.

But the bottom line is that there is enough political will in Nato now to do defence plans for the Baltic states. The opposition has melted away over the past 18 months," said Tomas Valasek, defence analyst at the Centre for European Reform. He worked with Madeleine Albright, the former US secretary of state, on drafting Nato's new "strategic concept" this year.In a meeting last December in Brussels with the Nato ambassadors from Poland, the three Baltic states and the Nato secretary-general, Anders Fogh Rasmussen, together with the US and German ambassadors, Ivo Daalder and Ulrich Brandenburg, secured agreement on the new policy.

"Ambassador Daalder acknowledged in these meetings that Germany had initiated the proposal," says another secret cable .The east Europeans were delighted. Paul Teesalu, a senior Estonian diplomat, described the policy shift as "an early Christmas present" when told last December in Tallinn, according to a cable.

Another secret report from the US embassy in Riga says the Latvian foreign ministry's security policy chief "expressed his government's profound happiness."

The Poles, although keen supporters of concrete Nato defence plans for the Baltic, were neverthless worried that the new policy could dilute alliance commitments to their defence, since a limited Polish contingency plan was being turned into an expanded regional blueprint for the four countries.

Poland's late deputy defence minister, Stanislaw Komorowski, told US diplomats in Warsaw that he was "sceptical that a regional approach was the best way ahead. Komorowski said Warsaw would prefer a unique plan for Poland.".

Komorowski, the Polish ambassador in London until 2004, was one of 98 people killed with the country's president, Lech Kaczynski, when their plane crashed at Smolensk, Russia, in April.

The Americans argued that adding defence planning for the Baltic states would reinforce rather than dilute Polish security.

"After two years, contingency plans have been successfully prepared for Poland," Bogdan Klich, the Polish defence minister told Warsaw newspaper Gazeta Wyborcza last month.

In January, after the decision was taken, the state department in Washington instructed US missions and embassies how to proceed, making clear that the drafting of defence blueprints for the Baltic was the beginning of a more ambitious overhaul of Nato's core military planning.

"This is the first step in a multi-stage process to develop a complete set of appropriate contingency plans for the full range of possible threats – both regional and functional – as soon as possible," said the secret cable.

The diplomatic traffic seen by the Guardian is from US state department and US embassies worldwide, but not from Pentagon or CIA communications, meaning that the cables reveal the policy and political decision-making processes but contain little on the specifics of hard military planning.

Details of the nine divisions earmarked for the plan and the prominence of the port of Swinoujscie, on Poland's Baltic coast, were leaked to Gazeta Wyborcza.

It is clear that the defence plans for Poland and the Baltic are to be orchestrated from Nato's Shape planning headquarters at Mons in Belgium and from the Joint Forces Command at Brunssum in the Netherlands, the nerve centre for overseeing the crucial German theatre during the alliance's cold war heyday.

The policy shift represents a sea change in Nato defence planning and in assessments of the threat posed by what a Polish official calls "a resurgent Russia."

Officially the US and Nato term Russia a "partner" and not an adversary, with the Germans, French, and Italians in particular tending to be deferential in dealings with Moscow. But the east Europeans, with their bitter experience of Moscow domination, argue that the Russians respect strength, despise and exploit weakness and division, and that Nato will enjoy better relations only if its most exposed and vulnerable members feel secure.

"The whole point is not to paint Russia as a threat. It is about reassuring those countries that are seriously worried.

The debate is primarily about Poland and the Baltic. Geography has a lot to do with it," said Valasek.

Repeatedly calling for the Baltic military plans to be kept utterly secret, Clinton and other senior US officials acknowledge that the policy shift "would also likely lead to an unnecessary increase in Nato-Russia tensions … Washington strongly believes that the details of Nato's contingency plans should remain in confidential channels."

John Naughton, page 27