WASHINGTON — Even as President Bush and Prime Minister Olmert pledged to prop up the Palestinian Authority president, Mahmoud Abbas of the Fatah Party, Congress is preparing to take new action against Iran, the state bankrolling Hamas — Fatah’s rival for power in Gaza.

Today, the House of Representatives is scheduled to vote on the 2008 foreign aid budget, which will instruct Secretary of State Rice to “undertake efforts to restrict the supply of refined gas to Iran in order to prevent Tehran from acquiring nuclear weapons,” according to a summary of the bill provided to The New York Sun.

The language in the foreign aid authorization, legislation that is expected to pass both chambers, would be to date the toughest measure America has taken against the Islamic Republic, which must import more than half its gasoline, despite having the third-largest known reserves of raw petroleum.

The measure against Iran reflects that Congress and the White House see Hamas’s successful coup in Gaza in part as a victory for Iran, the state that has provided both training and an annual $100 million budget to the Sunni Islamists considered terrorists by Israel and America.

The bold move also reflects the new political environment where contenders for the presidential nomination in both parties have advertised new policies to grapple with the threat from Tehran.

Yesterday, Fred Thompson — a former Tennessee senator and actor on the television series “Law and Order” — suggested during a speech in London that an international blockade of Iran might be a last resort to avoid military action against the mullahs.

“When the president of Iran shares his nightmare visions before cheering crowds, those are not just a fanatic’s version of an empty applause line. The only safe assumption is that he means it,” he warned.

Senator Obama of Illinois, a Democratic aspirant to the presidency, has also in the last month proposed a comprehensive set of bank sanctions on corporations and banks that still do business with Iranian entities.

The bold words from the presidential contenders, however, contrast sharply with America’s actual diplomacy toward Gaza and the West Bank.

President Bush yesterday praised Mr. Abbas — saying he is a man who has “spoken out for moderation” — even though Mr. Abbas only three months ago was seeking a power-sharing agreement with the Hamas Party, which last week was throwing his security service men off of rooftops.

Mr. Olmert concurred with Mr. Bush and promised to make every effort to cooperate with Mr. Abbas.

But for now, Mr. Olmert’s cooperation for will be focused not on the contours of a two-state solution, but rather on how to alleviate Palestinian Arab suffering. “I have to talk with him of the current issues that can help upgrade the quality of life of the people and provide them better security in the West Bank, and to share with him the efforts to calm the terror — this is something that he is absolutely committed to doing, we have to do it, and this is not something that the Palestinians can escape,” he said.

An American diplomat yesterday said one concern for Washington was the prospect that Hamas could play the role of spoiler in the West Bank, as Europe and America shower the new Abbas government with aid and diplomatic recognition. “There is a strong possibility that Hamas could assassinate Fatah leaders, and we have to be wary of that,” the official said.

Mr. Olmert also hinted that the closure of the border between Gaza and Israel would not impede the delivery of food and medicine to the isolated strip. “We have been very, very attentive to the needs of the — humanitarian needs of Gaza, and we will continue to provide everything that is necessary in order to meet these humanitarian needs. Israel will not be indifferent to the human suffering in Gaza,” he said.