WASHINGTON — The Democratic-controlled Congress is moving to outflank both the Bush administration and the United Nations with the toughest set of sanctions against Iran that have ever been proposed.

The introduction of the new legislation comes as more than 5,500 members of America’s largest pro-Israel lobby are set to arrive in Washington for their annual policy conference. They are expected to press Congress to endorse new legislation to sanction foreign companies that do business with Iran and to re-impose the import restrictions, on items such as rugs, pistachios, and caviar, which President Clinton lifted in 2000 to foster dialogue with an Iranian regime that was seen as reformist.

The goal of the sanctions is to deny Tehran funding that could be used to support terrorism and attacks on American troops in Iraq or to build nuclear weapons or missiles. With the United Nations hesitant to take significant action against Iran and even American allies in Europe hesitant to move beyond symbolic condemnations, the congressional actions are an attempt to signal to both Iran and its international business partners that Washington is running out of patience with Iranian misbehavior.

The new sanctions legislation introduced yesterday by Rep. Tom Lantos, the chairman of the House Foreign Relations Committee, differs from earlier sanctions bills in that it would not grant President Bush the authority to waive sanctions against oil companies that sign new agreements with the Islamic Republic.

The activists who will be pressing the new bill are coming to Washington for the annual convention of the American Israel Public Affairs Committee, where the House speaker Nancy Pelosi, a Democrat of California, is scheduled to give her first major speech on Middle East policy as the House leader. Both the Republican and Democratic leaders of the House and Senate will make speeches at the event, which is also expected to draw presidential candidates such as Senators Clinton, Obama, Biden, and Brownback. Senator McCain is said to be likely to attend as well.

Yesterday, Aipac spokesman Josh Block said the lobbying push this year has three priorities. To start, the group will try support “continued U.S. aid to Israel that helps strengthen American interest in the region by ensuring that our ally Israel remain strong and secure in it’s tough neighborhood.” That priority is important because the ten-year agreement signed between President Clinton and Prime Minister Netanyahu that phased out the economic assistance element of the $2.4 billion in annual aid Israel receives as a condition of its peace accord with Egypt is set to expire. Today Israeli and American diplomats are negotiating new terms of how the American assistance will be spent.

Mr. Block also said organization’s activists will be urging lawmakers to withhold aid from “going to support or legitimize a Palestinian Authority dominated by a terrorist group, Hamas, which refuses to recognize Israel, renounce violence or abide by previous agreements with the Jewish State.” That issue is particularly tricky for the Bush administration today because the Palestinian Arab president, Mahmoud Abbas, is currently in negotiations with Hamas, a State Department designated foreign terrorist organization.

The new focus for the organization this year will be Mr. Lantos’ new legislation. Yesterday at a hearing before his committee, Mr. Lantos laid down the gauntlet for international energy companies.

“Until now, abusing its waiver authority and other flexibility in the law, the Executive Branch has never sanctioned any foreign oil company which invested in Iran. Those halcyon days for the oil industry are over,” he said.

“If Dutch Shell moves forward with its proposed $10 billion deal with Iran, it will be sanctioned. If Malaysia moves forward with a similar deal, it too will be sanctioned. The same treatment will be accorded to China and India should they finalize deals with Iran,” said Mr. Lantos, a Democrat from California.

Mr. Lantos’s Republican counterpart on the House Foreign Relations Committee, Ileana Ros-Lehtinen, yesterday introduced her own Iran legislation mandating divestment by federal government pension funds from companies that have invested more than $20 million in Iran’s energy sector. The measure also expresses the Sense of Congress that private funds should also divest from such entities, prohibits future investments by either government or private pension funds, and requires publication in the Federal Register of a list of companies that have invested $20 million or more in Iran’s energy sector, in violation of the Iran Sanctions Act. Mr. Lantos said he expected that the law finally passed would incorporate elements of Ms. Ros-Lehtinen’s legislation.

For Aipac to endorse the legislation this year could place the bipartisan lobby on a collision course with a Bush administration that has used earlier bills supported by Aipac to sanction Iranian banks and front companies.

Yesterday, the undersecretary of State for political affairs, Nicholas Burns, said he supported the new sanctions in general, but that administration would oppose the loss of waiver authority because it would have the effect of forcing America to sanction its allies.

The new bill could also force America’s hand this weekend, when a top American diplomat, Ambassador Zalmay Khalilzad, participates in a meeting of ambassadors and diplomats in Baghdad that will include both Iran and Syria. Iran has come under pressure recently, with Interpol recommending arrest warrants for former Iranian officials in connection with the bombing of a Jewish cultural center in Argentina. The Bush administration has accused Iran of supporting bombings in Iraq, and the United Nations has said Iran is flouting international inspections of its nuclear program. The Telegraph reported today that an Iranian spymaster, General Ali Reza Azkari, went missing in Turkey last month and is suspected of possibly having defected to the West.

Mr. Block stressed that the annual policy conference this year was evidence of the “bipartisan nature of American support for Israel throughout the past and into the future regardless of which party is in control of the House or Senate, and the history, breadth and diversity of America’s centuries of support for the Jewish homeland in Israel.”

Nonetheless, some elements in the Democratic Party have worried Jewish leaders and the pro-Israel community. The American general who led NATO, a 2004 Democratic presidential candidate, Wesley Clark, in January told Web logger Arianna Huffington that he was confident America would bomb Iran because it was pushed by “New York money people,” and written about in the Israeli press. Also, the party’s 2004 vice presidential pick, John Edwards, has chosen a former congressman, David Bonior, as the manager of his 2008 presidential campaign. Mr. Bonior was one of the least friendly votes for Israel in the House when he was in Congress.