OTTAWA - Canada should bring its immigration laws into line with the United States to help combat terrorists in the wake of Tuesday's attacks on the World Trade Center and the Pentagon, Paul Cellucci, the U.S. Ambassador to Canada, said yesterday.

As speculation mounted that a number of the terrorists involved in the devastating air strikes entered the United States from Canada, this country's reputation for lax border security was assailed by Stockwell Day, the Leader of the Official Opposition, and by a former director of the Canadian Security Intelligence Service.

Mr. Cellucci did not directly criticize Canada's efforts to combat terrorism but he pressed for more consistent immigration policies to "establish a North American perimeter that would apply more rigorous controls for people landing from overseas," Mr. Cellucci told reporters in Ottawa.

"I do think it's one of the questions we have to address in the aftermath of [Tuesday's] events.... We need to defend the people of North America from these kinds of vicious attacks."

The counter-intelligence branch of CSIS has repeatedly warned that terrorists groups are using Canada as a base to raise money to purchase and deliver weapons, enhance combat training and provide logistical support for terrorists acts in other parts of the world.

These organizations, including groups linked to Hezbollah, Hamas, the IRA, Tamil Tigers, the Kurdistan Workers' Party and major Sikh terrorist groups, also use Canada as a safe haven and as an entry point into the United States.

Experts suggested that Washington will pressure Ottawa to adopt tougher immigration and security policies if a Canadian link is proven in the bombings.

"The United States will put pressure on us, as they have been doing, to adopt similar forms of restrictions as the ones they've got," said David Mutimer, of the Centre for International and Security Studies at York University in Toronto.

"I suspect we're going to have to move in that direction if we want to maintain some form of open border between the two countries."

"There are already indications in Toronto that the Tamil Tigers are raising money, if not recruits, for the ongoing quasi-civil war in Sri Lanka," added Jim Hanson, associate executive director of the Canadian Institute of Strategic Studies.

Still, Mr. Hanson said it would not be easy for Canada to bow to demands from Washington. "I think we have the same problem as they do. We are a free country; we are open to immigration; we're open to foreign trade and people can cross the border relatively easily."

Reid Morden, the former director of CSIS, said yesterday the Canadian government has taken "some baby steps to recognize there is a problem, but not on the fundraising side. There is much work to be done on that."

The U.S. government has raised concerns about Canada's lax security in the past, although Mr. Morden said there is also recognition Canada co-operates with information-sharing and other security measures.

"I think the people who are doing the work in the trenches are doing their job. Both governments know that," he said in an interview. "But at the very least the government is going to have to have a major review of its entry policies, and that includes its enforcement policies at ports of arrival and departure."

For example, Mr. Morden noted where Ottawa has privatized airports, security matters have often been handed off to local police forces.

"I wouldn't be surprised if there was some reassertion of federal presence there."

He warned there will be repercussions for trade with the United States if Canada is not seen to act.

"There is going to be a blip on the radar. Whether the blip will settle down at the level before will depend on how satisfied the Americans at all levels of government are ... that Canada is responding to just about the most horrific event since the last war."

Sergio Karas, a Toronto immigration lawyer, said Canada's "overly naive" policies must be revisited. "Canadian immigration policy has been deficient for quite some time," he said. "We are the laughingstock of the world because of our incredibly high acceptance rate for refugee claimants."

Mr. Karas suggested all undocumented travellers and those claiming to be refugees but with false passports should be detained. "This policy used to be the case," he said, adding it changed in the mid-1990s to arresting only those "who are danger to the public."

The government should also order the immediate expulsion of failed refugee claimants from countries such Afghanistan, Iraq, Iran and Lebanon, he added. "Failed claimants should be detained if they are high risk, because they otherwise disappear."

Janet Dench, director of the Canadian Council for Refugees, disagreed. "This is a very troubling knee-jerk sort of reaction to what are horrible events." She worried that people who are not security risks could get "caught up in the security net that currently exists" if laws are changed.

Elinor Caplan, the Minister of Citizenship and Immigration, could not be reached for comment yesterday.

Last March, she rejected Opposition demands to use electronic scanners at Canadian entry points to weed out terrorists, organized criminals and illegal immigrants and refugees.

Ms. Caplan told the Commons Immigration Committee she had concerns electronic scanning of passports -- used in many countries, including the United States -- would infringe on civil liberties and "hassle legitimate travellers."

Mr. Day, at a news conference yesterday in Ottawa, demanded an overhaul of Canada's immigration and security policies.

"We must ensure Canada will not be a target of terrorism nor used as a launching pad for terror against others," he said.

"This may mean greater security at our borders and our airports. It may mean laws to prevent foreign terrorists from living in Canada. It may mean laws dealing with using Canada as a fundraising centre for terrorist activity. It may mean offering military assistance to the United States and to our NATO allies in forming an international coalition against terrorism and against those who sponsor it," he said.

He said Canada still needs to encourage immigration, "but we also know ... that our screening techniques and our willingness to screen in an effective way those people who could prove dangerous, we know that is lacking."

Last month, Canada's intelligence service tied an Egyptian refugee claimant living in Tor- onto to the international Islamic terrorist network responsible for the fatal 1998 bombings of the United States' embassies in Kenya and Tanzania.

The arrest came amid growing concerns Canada is becoming an offshore base for Islamic-inspired terrorists such as Ahmed Ressam, the Algerian who lived in Montreal before attempting to bomb Los Angeles Airport.

CSIS has called Islamic extremists Canada's number one security threat.