The cosmopolitan city of Montreal has become easy pickings for Soviet agents who use it as a window into the complex and tightly secured net of United States defense operations.

Tagged by some as "the Vienna of North America" because of its popularity with East European spies, Montreal has become a home base for Soviet and other East Bloc agents in the guise of diplomats, trade representatives and a wide range of junior officers, according to Western intelligence sources.

In addition, intelligence experts in Ottawa say the Soviets and other East Bloc countries have successfully infiltrated the foreign affairs ministry, armed forces, scientific establishments and the news media.Canada's reputation for being an easy target for spies is blamed on the perceived ineptitude of the Canadian Security Intelligence Service, the country's civilian spy agency, set up four years ago after a series of scandals blackened the counter-subversion branch of the national police, the Royal Canadian Mounted Police.