Former White House deputy chief of staff Michael K. Deaver delivered a personal letter from President Reagan to President Chun Doo Hwan while Deaver was seeking to become South Korea's lobbyist here, a former U.S. ambassador to Seoul testified yesterday.

The assertion by Richard L. (Dixie) Walker appeared to contradict Deaver's claim that he never used his close friendship with Reagan to further the aims of the lobbying firm that he founded after leaving the administration in the spring of 1985.

Deaver's lawyers strongly challenged the testimony by Walker at Deaver's perjury trial in U.S. District Court here.

They asserted, over objections by prosecutors, that "no record of that letter has been found anywhere in the U.S. government or the government of Korea."

Walker, a University of South Carolina professor who was ambassador to Seoul from 1981 to 1986, insisted that Deaver had pulled such a letter from his pocket during a meeting with Chun at the Blue House, the Korean equivalent of the White House.

Told by Deaver lawyer Randall J. Turk that the Blue House had no record of the letter, Walker said, "So far as I know, the Blue House does not let you know what's there."

Earlier in the trial, a senior State Department executive testified that a search of department files did not disclose a copy of the letter.

Deaver is accused of lying to a congressional subcommittee and a federal grand jury about his contacts with high-ranking administration officials and attempting to obscure his role in a dispute with Canada about acid-rain pollution.

Drew Lewis, named special U.S. envoy to Canada on the pollution issue, testified yesterday that Deaver called him on the day that Reagan selected Lewis for the job and that he frequently talked to Deaver thereafter.

The reason, Lewis said, was that Donald T. Regan, then White House chief of staff, and the Office of Management and Budget were seeking to sabotage Lewis' effort to resolve the acid-rain controversy.

Lewis, a former transportation secretary, said he turned to Deaver, who served as a lobbyist for Canada, for advice on how to deal with his White House opponents.

"From time to time, I would indicate to him my frustration to the negative reaction I was getting from the administration," Lewis said.

Lewis, currently chairman of Union Pacific Corp., made no secret of his friendship with Deaver and his dislike for Regan and other White House foes.

Lewis said the president had told him to be "open-minded" about acid rain, on which the administration was split. According to previous testimony, some presidential advisers expressed concern that Lewis would commit the United States to a costly pollution-control effort.

When Lewis told New England governors soon after his appointment that he believed that the pollution was "injurious," he said, he noted that chief of staff Regan attacked him in the media, saying Lewis was not speaking for the administration.

Lewis said that he was merely restating long-established U.S. policy and that "it was clear that {Regan} didn't know what his government's position was."

Like virtually all of the ranking administration officials that Deaver is alleged in the five-count perjury indictment to have contacted, Lewis was vague on details of their conversations.

He said many of his chats with Deaver involved their joint effort to raise funds for a library to house Reagan's papers and that acid rain often was a secondary issue.

On cross-examination, Lewis conceded that he was uncertain who placed his telephone call with Deaver on March 14, 1985, the day that Reagan asked him to serve as acid-rain envoy.

Lewis said lobbyist Deaver made no attempt to influence his final report, issued in January 1986. But, during a breakfast meeting at the River Club in New York City, Deaver did suggest a change in the timing of its release, Lewis said.

Canadian officials at that meeting said they had hoped for a stronger recommendation by Lewis for increased U.S. funding to combat pollution. They also hoped that he would delay issuing the report until shortly before a forthcoming U.S.-Canadian summit.

But Lewis said the Canadians finally accepted his position, realizing that his position on acid rain was as favorable as they could hope to find in anyone in the administration.

Lewis said he was eager to end his role as envoy because his company, Warner-Amex Cable, had been sold and he was likely to join a major industrial firm. He said he feared that critics might link his new company to pollution and a conflict of interest "that would be embarrassing to the president or myself."

In late afternoon, prosecutors turned to Deaver's efforts to help the Boeing Co. win a contract to replace an aging presidential Air Force One aircraft with a 747 jet.

Brig. Gen. Matthew P. Caulfield, former deputy director of the White House Military Office, said he met with Deaver about it twice. Once, in Deaver's Georgetown office, he said, William Sittman, a Deaver associate, gave him a paper outlining ways in which the Air Force could improve the bidding process.

Caulfield, who said he believed that Deaver "wanted to be up front and forthright" on the issue, said he later threw the paper away. He said he told Deaver and Sittman that he was perfectly comfortable with military procurement procedures and would not attempt to change the process.