The judge presiding over the perjury trial of former White House aide Michael K. Deaver rejected a Justice Department plea yesterday to admonish Deaver's prosecutor for his attempt to get a Canadian diplomat to testify.

Saying he failed to see "anything wrong, unethical or improper" with the effort, U.S. District Court Judge Thomas Penfield Jackson brushed aside arguments that the attempt by independent counsel Whitney North Seymour Jr. to secure the testimony of Canadian Ambassador Allan E. Gotlieb had created an international incident. Jackson suggested that Canada may have "engineered" its own professed embarrassment over the incident.

The judge's comments came shortly after lawyers agreed on a panel of seven men and nine women to hear the five counts of perjury against Deaver. The panel, which includes four alternates, is expected to be sworn in this morning for a trial that the judge has said will last three to five weeks.

With the jury dismissed, the judge turned to what he called "the Canadian overture." The acrimony between Seymour and lawyers for Deaver, President Reagan's former deputy chief of staff, then resurfaced.

Despite arguments by Justice Department lawyer David Anderson and chief defense lawyer Herbert J. Miller Jr. that Seymour had threatened the Canadians, the judge sided with Seymour. He noted that the prosecutor's dealings with Stuart F. Pierson, a Washington lawyer for the Canadian government, apparently had that country's blessing and said the alleged threat to Canada was nothing more than typical language used by many lawyers.

In an Oct. 3 letter to Pierson, Seymour said he would 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" if Gotlieb did not testify.

Deaver, who counted Canada among his lobbying clients after he left the White House in 1985, was infuriated by the remark, his lawyer said, because it implied that he had committed crimes for which he hasn't been charged. "I say, your honor, it is wrong," Miller said, refusing to back down from his charge of improper conduct by the prosecutor.

The Canadian government, which earlier had asserted Gotlieb's diplomatic immunity from testifying, filed a formal protest with the State Department over the letter, noting that Jackson had quashed an effort by Seymour to subpoena the ambassador.

That protest triggered yesterday afternoon's request by the Justice Department that Seymour be ordered to send his communications with foreign countries through diplomatic channels and that he be

admonished for his letter to Pierson.

Jackson turned the requests aside, saying in effect that Canada had invited the prosecutor to communicate with it via Pierson. "It's Canada's choice" whether to communicate that way or through the State Department, the judge said.

Jackson also indicated that he will allow Seymour to introduce evidence about "other crimes" that Deaver may have been seeking to shield from investigators when he allegedly lied to a House subcommittee and a federal grand jury. The judge said he would, however, probably issue an order restricting the language that the prosecutor could use in describing the acts to the jury.