US congressional leaders and the most powerful pro-Israel lobby group in the US are attempting to forestall a significant shift in the White House's Middle East policy.

The move comes amid growing signs that the US president, Barack Obama, intends to press for urgent efforts to be made towards the creation of a Palestinian state.

The Israeli prime minister, Binyamin Netanyahu, is visiting Washington later this month amid growing expectations that Obama is preparing to take a tougher line over Israel's reluctance to actively seek a two-state solution to its conflict with the Palestinians.

It will be the first time that Netanyahu and Obama have met since both were elected.

The American Israel Public Affairs Committee (Aipac) this week sent hundreds of lobbyists to urge members of Congress to sign a letter to Obama.

The letter, written by two House of Representatives leaders, calls for Israel to be allowed to set the pace of negotiations.

The lobbying came despite critics saying Netanyahu has consistently failed to commit himself to the creation of a Palestinian state.

The letter calls for the maintenance of the status quo, with an emphasis on Palestinian institution-building before there can be an end to Israeli occupation.

It says the US "must be both a trusted mediator and devoted friend of Israel".

Aipac's move to put pressure on members of Congress came at the end of its annual conference in Washington this week.

Some of the loudest applause at the gathering came in response to calls for military attacks on Iran's nuclear facilities – something Netanyahu has attempted to portray as a more urgent issue than the Palestinian question.

But Aipac delegates were told by the US vice-president, Joe Biden, that the administration favours "mutual respect" in dealing with Iran.

Biden said the Israeli-Palestinian conflict strengthened Iran's strategic position and Israel must take concrete steps – including fulfilling often-broken commitments to stop the expansion of Jewish settlements – towards the creation of a Palestinian state.

Last week, General James Jones, Obama's national security adviser, told a European foreign minister that the new administration would be "forceful" with Israel, according to a classified Israeli memo reported by the Ha'aretz newspaper.

Jones was quoted as saying that Obama believes Washington, the EU and moderate Arab states must define "a satisfactory endgame solution".

"The new administration will convince Israel to compromise on the Palestinian question," he was quoted as saying. "We will not push Israel under the wheels of a bus, but we will be more forceful toward Israel than we have been under Bush."

During his election campaign, Obama alarmed Israel's hardline supporters by saying he regarded the lack of a resolution to the conflict as a "constant sore" that "infect[s] all of our foreign policy".

Netanyahu dare not openly defy Washington, and yesterday told the Aipac conference by satellite that he was ready for negotiations with the Palestinians.

But Aipac has moved to counter any new White House initiative by trying to mobilise Congress against it through the letter, written by two people seen as extremely close to the lobby group – Steny Hoyer, the Democratic majority leader in the House of Representatives, and Eric Cantor, the Republican whip.

The two men addressed an Aipac banquet attended by more than half the members of Congress on Monday, each standing in turn at a "roll call" of support for Israel.

On the face of it, the letter is a call for a peace, but its specifics urge Obama to maintain years of US policy that has tacitly accepted Israeli stalling of peace negotiations.

The letter says that "the best way to achieve future success between Israelis and Palestinians will be by adhering to basic principles that have undergirded our policy".

These include "acceptance that the parties themselves must negotiate the details of any agreement" as well as demanding that the Palestinians first "build the institutions necessary for a viable state" before gaining independence.

Jeremy Ben-Ami, the leader of J-street, a pro-Israel lobby group that favours the swift establishment of a Palestinian state, said that, while Aipac claims it supports a two-state solution, the letter is an attempt to prevent the White House from putting pressure on Israel to make that happen.

"They don't come right out and say we don't want Israel to make concessions, we don't want Israel to leave the West Bank," he said.

"They'll say, 'Of course we believe there should be peace'. But then they'll do what this letter does. "They'll say, 'When the Israeli government decides it is ready to have a two-state solution, then there'll be a two-state solution'."

Aipac wields considerable influence in the US Congress. Its critics say that what amounts to bullying pressure tactics has narrowed the room for debate about Israel, and claim the group has played a leading role in unseating some members of Congress who were critical of the Jewish state's policies.