aced with persistent and increasingly uncomfortable accusations that it has become an unwitting haven for terrorists, Canada is trying to shift its laws and practices to ease tensions with its neighbor.

The lower house of the Canadian Parliament gave quick approval last week to the first counterterrorism law in the country's history.

The parliamentary action came days before Canada's solicitor general, Lawrence MacAulay, and Attorney General John Ashcroft were to sign an agreement enhancing border security and take stock of the antiterrorism investigation in both countries. The two are scheduled to meet twice today, first in Detroit and then in Ottawa.

Mr. Ashcroft said on Sunday that he wanted to use several hundred National Guard troops and helicopters to improve patrolling of the 4,000-mile border between the United States and Canada.

Canadian officials, who have been fighting false rumors that some of the Sept. 11 terrorists crossed the border from Canada, hope the tough new law will prove that Canada is serious about fighting terrorism.

The measure, which is expected to be passed soon by the Senate, would vastly expand police surveillance powers and for the first time give Canadian law enforcement officials the ability to make preemptive arrests of suspected terrorists who might be preparing an attack. It also would allow police to hold suspects without charges for three days, up from the current 24 hours, and establish investigative hearings in which a judge could compel people to testify about terrorist plans.

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Even with the introduction of the new law, and with Mr. Ashcroft's acknowledgment in November that Canada has provided valuable intelligence information, a degree of irritation between the neighbors is likely to continue because their legal and immigration systems will still diverge in significant ways.

Anne McLellan, Canada's minister of justice, said there is a great deal of similarity between the two legal and immigration systems, but Canadian laws could do little to prevent terrorist acts from being planned or carried out. "We had not made the decision until recently to deal with terrorist activities as a discrete part of Canadian law," she said.

Several recent investigations of Canadian terror suspects underscore what are widely perceived in the United States as weaknesses in the Canadian system. Terrorism suspects are deported instead of being charged with crimes. Immigrants on police watch lists can roam freely for years before they have an asylum hearing. And local judges sometimes release suspects that the federal government is trying to extradite to the United States.

In one recent case, Canadian authorities took into custody a Syrian refugee accused of being a "bureaucratic terrorist" who helped provide money and forged identification documents to Al Qaeda, Osama bin Laden's network, but the only option open to authorities is to deport him.

In such cases, Canada does not bring charges or compel suspects to provide information. Rather, it relies on a proceeding that has been used fewer than a dozen times over the last decade. The Canadian Security Intelligence Service, Canada's spy agency, compiles a dossier against a suspect and presents the evidence, in secret, to a federal judge. The most serious action that can then be taken is for the judge to declare the suspect a threat to national security under the nation's Immigration Act. The suspect can then be deported.

In such a proceeding last month, authorities accused Hassan Almrei, 27, of supporting Osama bin Laden's terrorist network in several ways when he lived in Saudi Arabia and since he arrived in Toronto with a false passport from the United Arab Emirates on Jan. 2, 1999. He was accused of sending money to Mr. bin Laden's network through a honey and perfume business he ran in Saudi Arabia in the early 1990's.

Authorities said Mr. Almrei had direct connections to Nabil al Marabh, 34, who was arrested in the United States on Sept. 19 by the F.B.I., on suspicion that he may have been involved in providing false documents used by the Sept. 11 hijackers. Mr. Almrei's lawyer, Barbara Jackman, said she planned to appeal the deportation decision this week.

One of the biggest sources of friction between Canada and the United States has been Canada's treatment of refugees, who melt into Canadian society until called for a refugee hearing, at which they sometimes do not appear. In the United States, by contrast, asylum seekers are detained until their status is decided.

The United States began expressing concerns about Canada's asylum system after an Algerian refugee claimant from Montreal, Ahmed Ressam, was convicted of plotting to set off a bomb at Los Angeles International Airport during the millennium celebrations.

The Ressam case forced Canada to re-examine its counterterrorism efforts. Earlier this year, Canada overhauled its immigration laws to streamline the asylum application process so that it would not be possible for anyone to be free in Canada for four years without a final refugee hearing, as happened with Mr. Ressam. But some officials in the United States still say Canada's asylum law is not tough enough because detention is not mandatory.

In another recent investigation that points up ways in which the United States and Canada differ in fighting terrorism, proceedings are under way against Liban Hussein, a Somali man living in Ottawa whom American authorities have identified as a manager of an international money-transferring operation that funneled $3.8 million in cash to the Qaeda network. Mr. Hussein's brother, Mohammed M. Hussein, was arrested after the police raided the Boston office on Nov. 7.

Last month, a Superior Court judge in Ottawa released Liban Hussein on $8,000 bail. Mohammed Hussein is being held without bail on charges of running the cash transfer business without a valid license.

Ms. McLellan, the justice minister, said the federal government almost always opposes bail in such cases, but local judges sometimes grant it, just as in the United States.

"I certainly can understand why people in the United States are asking, `Why is one guy getting out on bail while the other is being detained?' " Ms. McLellan said. She would not comment further.