THE United States Embassy in Canada's capital, Ottawa, has some suspicious air vents and heat pumps on its roof. Maybe they're really part of the aging building's air system. But it's more likely that they hide antennas used to eavesdrop on Canadian government officials, claims a former Canadian spy.
Not that turnabout isn't fair play. In 1982, intelligence obtained by eavesdropping on the US ambassador helped Canada beat the US to a $2.5 billion wheat sale to China, according to the new memoirs of Mike Frost, ex-agent for Canada's Communications Security Establishment.
In the great game of international espionage, as this exchange shows, friendship can be relative. Western allies have long spied on each other for their own purposes, even as they shared secrets on other matters and worked toward such common goals as containing communism.
Thus recent charges of CIA work in France do not surprise experts. With the former Soviet Union no longer a target of overwhelming importance, spying among comrades might even be on the upswing. ''We have to be prepared to return to the kind of relationships intelligence services had before the cold war, when allies themselves had very complex relations,'' says Roy Godson, head of the National Strategy Information Center and a leading Washington intelligence analyst.
The Franco-American spy flap began waving last week, with a leaked report in the newspaper Le Monde that five Americans had been asked to leave France for allegedly spying on behalf of US intelligence.
The French government positions in trade talks and telecommunications policy were reportedly the primary American targets. Over the weekend, French and US officials played down the issue.
Given the nature of espionage, where enormous effort is expended to hide mysteries inside enigmas, it is unlikely that the full story of the incident will be known for years. Many in the US charge that the disclosure of the allegations was a domestic political move on the part of French Premier Edouard Balladur, meant to distract attention from troubles in his campaign for president.
''The essential point is the utter pettiness of the affair,'' says Angelo Codevilla, a Hoover Institution scholar and former Congressional intelligence-committee staff member.
Spying on friends common
Espionage of some sort among allies, points out Mr. Codevilla, is far from uncommon. The CIA maintains intelligence outposts in all major European countries -- as those nations undoubtedly do in the US. The CIA uses these stations to track international terrorists, for counterintelligence, to check on host-nation activities dubbed vital to US national interests. And the vast US infrastructure of electronic intelligence equipment, from spy satellites to embassy antennas, can be turned on friends as well as on foes.
This century there have been numerous instances of sensitive espionage operations carried out on friendly nations, point out experts. Among them:
* British spy operations in the US prior to World War I and World War II. Britain aimed to both sabotage German interests and push the US into war, through propaganda and other covert means.
*CIA involvement in Western Europe during the years of reconstruction after World War II. Worried about the rise of communist parties, the then-new agency secretly slipped cash to pro-American politicians. Almost $1 million was distributed during Italy's vote in April 1948.
*US eavesdropping on Britain, France, and Israel during the Suez crisis of 1956. The US National Security Agency cracked the military codes of all three nations to help track progress of the conflict in the Middle East, according to author James Bamford's classic study of the NSA, ''The Puzzle Palace.''
''Generally, spying is a means of last resort,'' when it comes to dealing with allies, notes Pennsylvania State University historian Charles Ameringer.
In recent years the intensity of international economic competition has driven much of the snooping among friends. According to former CIA director Robert Gates, the agents of some 20 nations now routinely spy on economic plans and industrial trade secrets in the United States.
CIA watches over US firms
Two years ago the CIA warned 49 US defense firms that France was after their technology, prompting some to pull out of the Paris air show. French intelligence may well have smarted at this public slap -- and planned its current tit-for-tat revenge.
US officials, for their part, insist that they do not spy directly on other nations' economic secrets. Rather, the CIA says, it conducts counter-intelligence to determine who is tracking US firms and tries to determine which nations are engaging in bribery or other unfair trade practices.
''This is a defensive or reactive process,'' claimed State Department spokeswoman Christine Shelly last week.