* Lithuania to be one of the few NATO nations to go beyond goal

* Money to be spent on acquiring weapons systems to deter Russia

VILNIUS, Sept 10 (Reuters) - Lithuania’s main political parties committed on Monday to increasing defence spending every year for the next decade, reaching at least 2.5 percent of gross domestic product by 2030.

U.S. President Donald Trump has railed against European allies for not spending enough on defence, and Lithuania’s expected investments will make it one of few NATO countries to go beyond an alliance target of 2 percent of GDP on defence.

But Lithuania’s main motivation is Russia’s annexation of Crimea from Ukraine in 2014, officials say, prompting the country to rebuild its military after years of neglect.

The country is on track to spend 2 percent of GDP this year, one of only eight of 29 NATO countries to do so. Before the Crimea annexation, it spent just 0.8 percent of GDP on defence in 2013, the second-smallest share of NATO countries after Luxemburg.

“Reaching the 2 percent spending target allowed the military to somewhat recover its capabilities,” Defence Minister Raimundas Karoblis told reporters at a signing ceremony in the prime minister’s office.

“Reaching the 2.5 percent threshold would allow it to develop real deterrence and defence capabilities, which is very important in today’s situation”, he added.

Of the seven parties in the parliament, five parties signed the agreement. Another said it would sign later, leaving just one party, the left-wing Social Democrat party, to reject the deal because it seeks spending on social issues, not defence.

The political agreement, which is not legally binding, makes defence spending increases part of every future government, whatever its political leaning.

The agreement calls for the country to acquire short-range and mid-range air defences and to reach a decision on whether to begin universal conscription by 2022. It will spend at least 30 percent of its defence budget buying arms in the next several years.

Lithuania, which already has U.S. and other NATO forces patrolling its territory to deter Russia, will work to maintain that presence, the agreement said.

Lithuania, together with its Baltic neighbours Latvia and Estonia, are significantly smaller than Russia, their former overlord, and rely on U.S. and NATO for their security.

Russian President Vladimir Putin suggested last month that NATO forces in eastern Europe posed a threat to Russia, a charge rejected by NATO officials.

NATO agreed in 2014 that each member would move towards boosting military spending to 2 percent of its gross domestic product by 2024. Cumulative expenditure by Europe and Canada has risen by almost $90 billion since 2015.

But only two-thirds of the allies, excluding the United States, have a realistic plan to hit the 2 percent level in 2024, NATO diplomats say. The United States spent 3.57 percent of GDP on defence in 2017. (Reporting By Andrius Sytas; editing by Robin Emmott, Larry King)