The Soviet Union declared yesterday that Canada's expulsion of 13 Soviet officials on spy charges was "provocative" and "absolutely groundless," but did not indicate whether it would retaliate by expelling Canadian diplomats.

Canadians Prime Minister Pierre Elliots Trudeau, for his part, said the "discovery of the spy ring" would make relations with the Soviet Union "more difficult . . . but I don't see it as the end of our relations in any sense."

Trudeau said be expected the Soviet secret police, the KGB, to continue trying to function in Canada.

"This operation will continue spying and we will continue trying spying and we will continue trying to prevent them," he told a new conference.

The Canadian government announced Thursday that it was expelling 11 Soviets - and had told two others who already had departed not to return - for trying to infiltrate the intelligence branch of the Royal Canadian Mounted Police (RCMP).

In reaction, the official Soviet news agency Tass, balmed "special services of Canada and the forces supporting them" for taking "hostile actions to complicate relations between the two countries," Washington Post correspondent Kevin Klose reported from Moscow.

Tass suggested that the explanation lies in current internal problems of the Canadian police, whose "reputation as reported by the Canadian press itself has become quite tarnished."

The RCMP, Canada's equivalent of the FBI, is the subject of two investigations into its spying on Quebec separatists several years ago.

Igor Lobanov, a Soviet Embassy press officer in Ottawa, said the "laughable accusations . . . will make easier the life of the RCMP now. They will get good press coverage from now on."

Trudeau called this "cynical speculation" and added in an ironic tone: "I'm sorry this is going to give a good image to the RCMP and its efficiency. Too bad it is happening at this time in an election year. Maybe the Soviets are trying to help the government."

Actually, elections do not have to be called until next year although it has been widely speculated that Trudeau will call them sooner.

Some press commentators in Canada did ask why such a fuss was made of the spy plot when it apparently was nipped before any damage to security. The only Canadian said to be involved was a police officer who helped trap the Soviets by accepting $30,500 for falsified information.

The Soviets allegedly sought information on how the police kept tabs on the activities of their diplomats in Canada. Press reports suggested that the Soviets were alarmed by a series of actions against Soviet and other Communist envoys accused of spying in recent years.

Several had been expelled previously without Soviet retaliation and External Affairs Minister Don Jamieson said Thursday that Canada would reply on a "one-for-one" basis" if Canadian personnel are now told to leave Moscow.

According to the Canadians, the policeman who broke the ring received intricate instructions and paraphernalia for rendezvous.

The Soviets were said to provide hollow canes and special cigarette packs for passing messages, and to call for signals with carefully placed orange peels.

Color signals were posted in a suburban Ottawa Shopping center, according to United Press International, with the policeman receiving these Soviet instructions: "Sing: a thin half; inch tape. Vertical position of tape - operation takes place in Montreal; horizontal position - operation takes place in Ottawa. Yellow color - call for the regular meeting. Black color - call for the instant meeting . . . Red color - call to stop any operations."

Another document called for a meeting at Old Chelsea, 15 miles from the capital. The double agent was to park and wait for a contact to say: "Can you show me the way to Pink Lake?" He was to answer: "Sorry, I know Pink Lake but in Ontario Province."