Al Qaeda "sleeper cells" in Canada and the United States have communicated with each other as recently as this month, probably to plan terrorist attacks in the United States, Canadian intelligence experts said yesterday. The disclosure came in the wake of the arrest last week of a pizza delivery man in Ottawa who is suspected of being associated with the terrorist network of Osama bin Laden.

Canadian authorities decided to arrest Mohamed Harkat, 34, shortly after he made calls to suspected al Qaeda members in the United States, said Reid Morden, former director of the Canadian Security Intelligence Service, who has been in contact with the Canadian spy agency on the matter. Morden confirmed comments made earlier by Canadian officials speaking on condition of anonymity.

Canada's normally secretive spy agency alleged in a rare court filing that Harkat, 34, who was born in Algeria and has lived in Canada since 1995, is an associate of Abu Zubaida, one of Osama bin Laden's close associates. Zubaida, who was arrested in Pakistan in March and is in U.S. custody at an undisclosed location, identified Harkat to his interrogators, according to Canadian intelligence officials.

The Harkat case is the most recent example of a historically close intelligence relationship between the two countries that has become unprecedented in its intensity as Canada and the United States work to thwart a global terrorist network adept at crossing national borders.

It was not clear precisely what triggered the arrest of Harkat. The nature of the phone calls to the United States with other al Qaeda members is also not known. But Canadian officials believe Harkat is a "sleeper" agent of al Qaeda. Sleepers, according to the court report filed by the spy agency, "are established in foreign countries for extended periods of time, up to several years, prior to a given operation being executed. Preceding the operation, they may live as regular citizens, leading unremarkable lives, and avoiding attention from local authorities."

The report said that al Qaeda members living in Canada fought alongside Arab Islamic militants in Afghanistan, Bosnia and Chechnya and trained in al Qaeda camps. Monitoring and arresting members of sleeper cells in the United States is the FBI's top priority. FBI Director Robert S. Mueller III has said the bureau has tripled the number of investigations and quadrupled the number of wiretaps against suspected al Qaeda supporters since Sept. 11, 2001. While critics say the FBI does not have a good grasp of the dominant cells in the United States, the bureau counters by pointing to cells it says it has broken up through arrests in Detroit; Lackawanna, N.Y.; Seattle; Portland, Ore., and elsewhere.

While the focus of U.S. military and CIA operations has been in such far-off countries as Afghanistan, Yemen and Indonesia, neutralizing the potential terrorist threat in Canada remains a top priority, said U.S. government officials. With that in mind, the CIA has increased the number of case officers in Canada by an undisclosed number. The FBI has also increased its presence at the U.S. Embassy in Ottawa and elsewhere.

According to Canadian officials, the CIA and FBI have swamped Canadian intelligence and law enforcement authorities with requests to conduct surveillance and investigations into suspected terrorists on Canadian soil. Both U.S. agencies believe the threats are directed at the United States.

The Canadians "don't have the personnel to cope with the material that the CIA and intelligence community is processing in the United States," said Wesley Wark, an intelligence expert and professor at the Munk Centre for International Studies at the University of Toronto. "There is a great deal more flowing in the form of intelligence from the south to the north. People are not complaining about it," they are saying "we need more resources in the intelligence sector."

Canada has responded, in part, with a 30 percent increase in its intelligence budget, an unparalleled campaign to hire new intelligence officers, and judicial changes aimed at streamlining the arrest and deportation of suspected terrorists.

Canada and the United States last week signed an agreement giving U.S. police instant access to Canadian criminal records, and vice versa. The two countries have also agreed to substantially increase joint immigration and inspection activities along the 4,000-mile U.S.-Canadian border, and to substantially increase electronic surveillance there as well.

In the most aggressive and unusual case to date, Canada agreed to hand over to U.S. authorities without judicial proceedings a Canadian arrested this year in Oman, a top Canadian intelligence official confirmed. Mohammed Mansour Jabarah, a native of Kuwait, is accused of organizing a plot to blow up the U.S. and Israeli embassies in Singapore. He is being held in a secret location in the United States, where he is cooperating and revealing information about terrorists' plans, U.S. officials said. Publicly, Canada has said that Jabarah voluntarily agreed to go to the United States for questions.

In an equally unusual move, Canadian intelligence officers this year testified in an American court case against members of a suspected Hezbollah cell operating in Canada but who were arrested in North Carolina.

In a Nov. 7 speech, Ward Elcock, director of the Canadian Security Intelligence Service, Canada's domestic spy agency, said it was investigating 50 suspected terrorist organizations and "300 individual targets."

The first tip-off of the magnitude of Canada's terrorist problem came with the arrest in December 1999 of Ahmed Ressam, who was caught crossing the U.S.-Canada border as part a plot to bomb the Los Angeles International Airport during the millennium celebrations.

Other reminders that Canada might be playing an unwitting role as a safe haven for terrorists have come with arrests around the world of suspected terrorists carrying Canadian passports.

Last Thursday in Lahore, Pakistan, the FBI and Pakistani police arrested two Americans and a Canadian, Usman Khawaja, for their suspected link to al Qaeda.

According to the Canadian intelligence agency report, filed Dec. 10 in federal court in Canada, Harkat is from Taguine, Algeria. He was living in Ottawa, where he was married and working as a gas station attendant and a pizza delivery man when he was arrested.

The report alleges that Harkat came to Canada on Oct. 6, 1995, arriving in Toronto from Malaysia via the United Kingdom. He was using a fake Saudi passport. (The Canadian agency says that Saudi passports were "the document of choice for Islamic extremists wishing to enter Canada. Before 2002, Saudi passport holders did not require a visa to come to Canada.")

Harkat told Canadian officials that he was fleeing persecution by the Algerian government and was granted refugee status on Feb. 24, 1997. He applied for permanent residence on March 18, 1997, but the application was not completed because there were security and criminal checks to be done, according to the report.

Officials say that in Harkat's claim for refugee status, he acknowledged that he supported and was a member of the Front Islamique du Salut (FIS) in Algeria. That group was outlawed by Algeria in 1993.

Harkat fled Algeria in April 1990 and traveled to Saudi Arabia on a visitor visa, then on to Pakistan, where he remained until September 1995.

The Canadian agency says that Harkat also claimed loyalty to the Armed Islamic Group, which seeks to establish an Islamic state in Algeria "through the use of terrorist violence" and wants "to eliminate Western influences from the country."

Officials here say that Harkat's allegiance to the group is "an indication of support for the use of terrorist violence."

Researcher Margot Williams contributed to this report.