Independent counsel Whitney North Seymour Jr. has told the Canadian government that unless Ambassador Allan E. Gotlieb testifies at the perjury trial of former White House aide Michael K. Deaver, prosecutors will be "forced . . . to place much greater emphasis at trial on the unlawful acts engaged in by Deaver when he was working for the Canadian government."

Seymour, who tried to subpoena Gotlieb earlier this year, renewed his attempts to obtain the ambassador's testimony in an Oct. 2 letter to Stuart Pierson, a lawyer advising Canada. The letter has triggered outraged protests from the Canadian government, the State Department and the Justice Department.

The Canadian Embassy, in a blistering complaint to the State Department last Friday, called the letter a "shocking and extraordinary tactic" and said it "wishes to protest in the strongest terms this attempted intimidation." External Affairs Minister Joe Clark, in a statement released by the embassy, here, assailed Seymour's action as "outrageous."

State Department legal adviser Abraham D. Sofaer yesterday wrote Deputy Attorney General Arnold I. Burns, saying that Seymour's actions "have caused considerable embarrassment to both the governments of the United States and Canada."

Justice Department spokesman Patrick S. Korten said Seymour had violated departmental guidelines and an earlier agreement, reached after his attempt to subpoena Gotlieb, that approaches to foreign governments would be made through diplomatic channels.

"We will go to the court and ask them to insist that that agreement on his part be abided by," Korten said. "We're not exactly delighted about it."

Seymour declined to comment yesterday, saying, "It is obviously a private letter." Randall J. Turk, one of Deaver's lawyers, said he was surprised and unaware of the letter.

Deaver is to go on trial Monday on five counts of lying to a grand jury and a House subcommittee. One of the counts alleges that Deaver lied to the grand jury about the extent of his involvement with the acid-rain problem before he resigned as deputy White House chief of staff to work as a lobbyist.

In June, U.S. District Court Judge Thomas Penfield Jackson quashed Seymour's attempt to subpoena the ambassador and his wife, Sondra Gotlieb, to testify at Deaver's trial, ruling that Gotlieb was shielded by diplomatic immunity and had not waived that immunity by agreeing to answer written questions from Seymour.

Seymour argued that Gotlieb is a "key prosecution" witness whose testimony is "essential." The indictment alleges that Deaver falsely testified that he did not recall a Jan. 5, 1985, luncheon with the Gotliebs, which occurred while Deaver was still at the White House and the United States and Canada were preparing for a summit at which acid rain was to be a major issue.

"The stark fact is that there are no available witnesses to testify about Deaver's crucial luncheon meeting," Seymour said in court papers. "Only four persons were present: Mr. and Mrs. Deaver and Mr. and Mrs. Gotlieb . . . . Mrs. Deaver cannot be expected to testify against her husband. That leaves exactly two witnesses: Ambassador Gotlieb and his wife."

In the letter to Pierson, Seymour said the Canadian government's refusal "to permit even limited testimony by Ambassador Gotlieb has forced us to place much greater emphasis at trial on the unlawful acts engaged in by Deaver when he was working for the Canadian government, including his various contacts with Drew Lewis {President Reagan's envoy on acid rain} and the River Club meeting on Oct. 25, 1985, in which Mr. Gotlieb and Mr. {Fred} Doucet {an aide to Prime Minister Brian Mulroney} participated."

The indictment alleges that Deaver, while in the White House, "actively supported" the choice of Lewis for the post. After he had left the White House and was working for Canada, Deaver attended the meeting at the River Club in New York at which Lewis and his Canadian counterpart discussed acid rain.

"If you see any sign that your client might allow Mr. Gotlieb to give limited testimony confirming the January 5 luncheon, making it unnecessary for us to emphasize these other events, please get in touch with us promptly," Seymour wrote.

Pierson said Gotlieb will not testify. When the issue last arose, he said, "Seymour was told in no uncertain terms that the Canadian position wouldn't change. And that's still the position, particularly considering the attempt at intimidation."

The Deaver case has long been a political headache for the Mulroney government, with some in Ottawa questioning the propriety of hiring Deaver to help Canada seek U.S. controls on acid rain. After leaving the White House in May 1985, Deaver obtained a $105,000-a-year contract with the Canadian government.

Seymour initially investigated whether Deaver violated federal conflict-of-interest laws barring certain official from ever lobbying on matters in which they personally and substantially participated and prohibiting them from lobbying their former agencies for one year. However, Deaver was ultimately indicted only on perjury charges.

In the protest filed with the State Department, the Canadian Embassy said the charges against Deaver "do not relate to his activities under that contract and in no way implicate the government of Canada."

Seymour, the embassy said, "clearly expects that by threatening to 'convict' Canada of nonexistent offences in the publicity surrounding a trial in which Canada is not a party, he will succeed in intimidating the Government of Canada and compel it to give up its rights under international law."

Staff writer Bill McAllister contributed to this report.

Independent counsel Whitney North Seymour Jr. wrote Oct. 2 to Stuart Pierson, a lawyer representing the Canadian government, seeking to obtain the testimony of Canadian Ambassador Allan E. Gotlieb at the perjury trial of former White House aide Michael K. Deaver.

While in the White House, Deaver allegedly urged that Drew Lewis be appointed a special envoy on the acid-rain issue. Later, while working as a lobbyist for Canada, Deaver attended a meeting at the River Club in New York at which acid rain was discussed.