WASHINGTON -- President Bush plans to impose sanctions on Syria to pressure it to halt support for terrorist groups, sending a strong message to President Bashar Assad as foreign fighters continue to cross into Iraq from Syrian territory, senior governments officials said yesterday.

The officials also said Jordanian investigators have reported that chemicals discovered in a foiled Al Qaeda plot in Jordan had been smuggled in from Syria.

The White House has told members of Congress that as early as this week the president will implement the Syria Accountability and Lebanese Sovereignty Restoration Act, passed overwhelmingly by both houses of Congress and signed into law in December...

The law gives Bush new leeway to punish Syria economically and diplomatically for failing to act forcefully against terrorism. The sanctions could include prohibiting the sale of American products and US investment in Syria and restricting the travel of Syrian diplomats in the United States. It was not immediately clear yesterday which sanctions Bush would invoke.

''The word I have gotten from the administration is the president fully intends to implement it," Representative Elliot Engel, Republican of New York and a key sponsor of the legislation, told the Globe yesterday.

Such a move is expected to increase anti-American sentiment in the region, already heightened over the war in Iraq and Israel's recent assassinations of two Hamas leaders, as well as Bush's support for Israeli Prime Minister Ariel Sharon's plan to keep some West Bank settlements.

Engel and others said the White House was waiting to take action against Syria after a series of meetings in Washington this month with Middle East leaders, including President Hosni Mubarak of Egypt, Sharon, and King Abdullah of Jordan. Jordanian officials announced yesterday that Abdullah, who was scheduled to meet with Bush at the White House tomorrow, has postponed his trip until next month.

''I think there is something we might hear this week," said Theodore Kattouf, who served as Bush's ambassador to Syria until last fall and met with the Syrian president last week. He added, however, that recent developments could delay the move.

Syria, labeled by the State Department as a sponsor of terrorism for its support of anti-Israeli terrorist groups such as Hamas, Islamic Jihad, and the Lebanese Hezbollah, has come under enhanced scrutiny in recent days. US forces have been battling with armed insurgents in western Iraq who are believed to have infiltrated the country through Syria. Five US Marines were killed Saturday in the western Iraqi town of Husaybah.

Secretary of State Colin L. Powell told the Associated Press yesterday that he has asked Syria to beef up security on the border. ''It is in our mutual interest to deal with the problem," Powell said. ''It is not in Syria's interest to be seen as a base from which infiltrators can come across to kill innocent Iraqis or to kill coalition troops."

The Syrian Embassy did not return calls yesterday seeking comment on the allegations.

General Richard B. Myers, chairman of the Joint Chiefs of Staff, said Sunday that ''We know that the pathway into Iraq for many foreign forces is through Syria. It's a fact. We know it. The Syrians know it." Myers, speaking on CNN's ''Late Edition," said, ''The Syrians need to take this situation very seriously. They need to help us stop that infiltration of foreign fighters. It doesn't do their government any good."

Meanwhile, Jordanian authorities announced Saturday that raids earlier this month uncovered an Al Qaeda cell in Jordan that was planning to detonate a huge chemical bomb at the headquarters of the Jordanian Intelligence Services, the US Embassy, and other targets in Amman. They said the raw materials could have killed as many as 20,000 people in gas attacks.

''There is evidence that it came from Syria into Jordan," Engel said of the chemical materials and explosives. ''The Jordanians believe that and I believe that."

But Kattouf, who met with Assad last week, said Syria has little incentive to cooperate with the United States in policing its border with Iraq or other issues in the current environment,

On border control, ''I believe last October the Syrians, through their ambassador, let it be known that they might be open to some cooperation," said Kattouf, president of America-Mideast Educational and Training Services, a private nonprofit organization in Washington. ''I conclude that some elements of the [Bush] administration are so anti-Syrian that they would prefer to issue public warnings rather than to open serious talks on the matter."

The Syria Accountability Act called on Damascus to ''immediately and unconditionally halt support for terrorism, permanently and openly declare its total renunciation of all forms of terrorism, and close all terrorist offices and facilities in Syria." It also demanded that Syria pull its military forces out of neighboring Lebanon, which it has occupied for more than two decades.