After hockey, the favorite Canadian pastime, it appears, has been eavesdropping.

Deputy Prime Minister Erik Nielsen confirmed in the House of Commons last week published reports that during the 1960s he had learned, "word for bloody word," what was being discussed in the weekly opposition Liberal Party caucus through electronic surveillance.

A day earlier, a Canadian legal commission reported that twice as many wiretaps are authorized by judges in Canada as are approved in the United States. "It is astounding that this country has recorded on a per capita basis more than 20 times the number of authorizations as our massive American neighbor," the Law Reform Commission of Canada said in a statement released with its report.

Nielsen's admission was another blow to the accident-prone Conservative Party government of Prime Minister Brian Mulroney, which has been pummeled with one little scandal after another the past five months, keeping him pressed to the ropes.

Although he apologized on Monday, after the disclosure had dominated the news here for four days, Nielsen initially had tried to defend himself by saying he had not initiated the bugging.

Nielsen said wires had been crossed accidentally when a new electronic translation system was installed in Parliament. But he acknowledged reading verbatim reports from the eavesdropping and having had translations made for comments in French.

Mulroney has seemed typically unable to settle on any firm strategy for handling the latest brouhaha.

The eavesdropping incident has followed a string of others, including the resignations of three Cabinet ministers after charges of improprieties and the so-called "tunagate" affair in which his government overruled inspectors and allowed thousands of cans of rancid tuna to be sold in supermarkets.

Over the weekend, Mulroney had tried to play down Nielsen's confession of eavesdropping, saying it was similar to someone walking by an open window who "hears himself and his family being savaged and his reputation being attacked. I suppose you would have to not be human not to listen."

Another longtime Conservative legislator, Alvin Hamilton, adopted a similar defense, comparing it to listening in on party telephone lines, which are still common in Canada. He drew a moral distinction.

"If you listen, you're just ordinary," Hamilton told the Toronto Globe and Mail newspaper. "But if you go around repeating what you heard to other people, . . . that was considered improper. No one, to my knowledge, publicly in the Conservative Party at any time has ever said what they learned."

As Liberals and members of the New Democratic Party, the other principal opposition grouping, gleefully seized on the Nielsen admission and called for his resignation, virtually no attention was paid to the reports of warrants for legal wiretapping, which the independent law commission characterized as "an unjustified pervasiveness of a very intrusive device."

In 1981, for example, the commission found that 1,059 warrants were issued in Canada compared with 589 in the United States. It faulted the Canadian system for not employing safeguards to privacy, such as requirements that monitoring devices be turned off except during conversations pertinent to the subject of the court order. A typical Canadian police wiretap "acts like a huge electronic vacuum cleaner, indiscriminately sucking in the relevant with the irrelevant without distinction," the report said.

A government commission studying the practices of the Royal Canadian Mounted Police determined a few years ago that they had been responsible for numerous wiretaps without court authorization, findings that led to a restructuring of the Mounties.

Although Liberal Party members have been indignant publicly about the Nielsen affair, indications are the Conservatives have had no patent on eavesdropping.

Quebec Liberals acknowledged a year ago that they routinely had used simple radio scanners and car telephones to eavesdrop on calls by ministers in the then-ruling Parti Quebecois from their limousines. Pierre Paradis, a Liberal Party member of the Quebec legislature, confirmed the practice for the Canadian Press.

"It's perfectly legal," Paradis said. "There is nothing special about it. Anyone can do it. Just sit in a car which has a telephone and you can pick up hundreds of conversations. Anyone who has a telephone in his car knows that . . . . The PQ ministers are the only ones who don't know it."

Ironically, Nielsen had complained bitterly a year ago in an interview with the Canadian magazine, Saturday Night, that the Liberals had tapped his phone and intercepted his mail in the 1960s and early 1970s. He said the eavesdropping had worried his wife Pamela and contributed to the detrioration of her health. She died in 1969.

But in the same interview, he also acknowledged that the eavesdropping was not all one-sided, boasting, "We knew every word that was spoken inside" Liberal Party caucuses because of crossed wires in the parliamentary electronic system.

That account caused little stir. It was not the first time Nielsen had told the story. In 1973, he revealed it in a tape-recorded interview with author Peter Stursberg, who was researching a book on former prime minister John Diefenbaker. At Nielsen's request, Stursberg left it out of his book, "Diefenbaker: Leadership Lost 1962-67."

But Stursberg gave the tape of the interview to the Public Archives of Canada in Ottawa. Last Thursday, the Toronto Star, saying it had "found" the tape there, reported what the newspaper described as "the startling revelation," creating an instant sensation in the Canadian capital -- and a new minicrisis for Mulroney.