WASHINGTON -- For Jean Chrétien, defusing the economic threat of a less porous Canada-U.S. border is simply a question of distinguishing between people and trucks. If only.

A reporter asked the Prime Minister yesterday after his White House meeting with U.S. President George W. Bush whether there was any real danger that increased border security measures would endanger the free flow of goods between the two countries.

Absolutely not, Mr. Chrétien replied.

"They will not stop the security of the border for the trade," he said. "They want the trucks to move as quickly as before, both ways."

Leaving aside the security implications of checking people but not trucks, experts in both countries warn that Mr. Chrétien's optimism seriously underplays a growing danger that the transparent border between the United States and Canada might soon become more opaque, damaging both economies and exposing Canada's declining influence inside Washington.

"For Canada, this is a major, major problem," worries Jack Mintz, president of the Toronto-based C. D. Howe Institute.

Chris Sands, a Canada-U.S. specialist at the Washington-based Center for Strategic International Studies, believes that stiffened border controls would be yet another example of Canada's "diplomacy of decline."

Both the U.S. and Canadian economies depend on an open border. One quarter of U.S. exports are destined for Canada, while 85 per cent of Canadian exports head south. In a world of just-in-time delivery, that trade depends on the problem-free transit of planes, trains and trucks.

Border delays would harm productivity, encourage transnational corporations to retrench to their home country and threaten globalization beyond the dreams of a Seattle protester.

Yet the United States may be willing to take the risk.

Mr. Mintz believes the Americans will demand proof that Ottawa is acting aggressively to combat possible terrorist infiltration.

Tightening security at airports won't be enough. Canada will be expected to invest heavily in police, intelligence and security agencies. It will be expected to provide the fullest co-operation with U.S. investigations into possible terrorist links, even at the politically charged risk of violating privacy legislation and constitutional protections.

The United States will also expect Canada to impose much stricter limits on the freedom of refugees seeking asylum in Canada. Canadian courts, however, have already declared that the rights of refugees are protected under the Canadian Constitution.

In that case, Mr. Mintz speculates, "it might force the Canadian government, for the first time, to really consider invoking the notwithstanding clause."

The more Draconian demands could be deflected if Canada enjoyed its traditional intimate relations with its U.S. partner. But as the teapot tempest over Canada's omission from Mr. Bush's address to Congress demonstrates, Canada is not top-of-mind right now, even if Mr. Bush did declare yesterday that getting a phone call from Mr. Chrétien "was like getting a phone call from a brother."

Canada's waning influence inside the Bush administration may be a matter of more than a Republican government obsessed with Mexico and, belatedly, Europe, rather than with English North American relations.

Canada, Mr. Sands observes, accepted rather than championed the North Atlantic Treaty Organization's invocation of Article Five, declaring the World Trade Center and Pentagon attacks to be attacks on all NATO states. It deferred to Brazil in the declaration by the Organization of American States of solidarity with the United States.

In other words, Canada, once a respected and influential voice within the U.S. sphere of influence, is now a largely passive spectator.

One unintended consequence of that passivity may be to make it harder to cajole the Americans into exempting Canada from tougher border controls, simply because it will be harder to get their attention.

Bilateral co-operation remains excellent. Canadians are as anxious as Americans to increase domestic security. Perhaps, as this campaign against terrorism evolves, Canada's true commitment and solidarity will become more evident.

It will have to, if Canada wants to remain a brother.