Former White House chief of staff Donald T. Regan yesterday contradicted Michael K. Deaver's sworn testimony that Deaver did nothing to push for appointment of Drew Lewis as a special envoy to resolve a dispute with Canada over acid-rain pollution.

Regan's surprise statement that Deaver told President Reagan in the Oval Office that he favored Lewis' appointment came during the 10th day of testimony at Deaver's trial on five counts of perjury. His testimony seemed to catch the defense off guard.

Prosecutors also produced a White House memorandum in which a lawyer said Deaver told him that he had "pushed" for selection of Lewis while Deaver was White House deputy chief of staff.

"I don't recall his precise words," Regan testified in U.S. District Court, "but I recall he was in favor of a special envoy, and he favored Drew Lewis."

Regan also gave a terse account of his futile efforts to block a representative of the South Korean government, a client of Deaver's lobbying firm, from seeing the president.

Deaver, who left the White House in the spring of 1985, is accused of lying to a congressional subcommittee and a federal grand jury about his role in Lewis' appointment and the extent of his lobbying contacts with high administration officials.

At issue is whether Deaver used his White House contacts to obtain entry to the Oval Office for Kim Kihwan, a South Korean trade representative seeking to present a letter to President Reagan.

Yesterday, Regan said he attempted to strike the Kim visit from the president's calendar when he first learned of it, about seven to 10 days before the visit Oct. 2, 1985.

"I objected; I said the president didn't have time," said Regan, explaining later that he feared that the visit would set a precedent and that special envoys from every nation would seek appointments with the president.

"Several days later, to my astonishment, it {the visit} was still" on the president's calendar, Regan said. "I was told the NSC {National Security Council} wanted it. I said, 'I don't give a damn. Get it off.'

"Twenty-four hours later, it was still there, and I hit the overhead," Regan said, using the Navy term for a ceiling.

Regan said an aide told him that Rear Adm. John M. Poindexter, then deputy national security adviser, would see him about the meeting. He said Poindexter later came to his office and requested that the meeting be allowed, contending that it was "important for good diplomatic relations as well as saving face" with Korea.

"I said, 'I can't see it, and we're setting a terrible precedent . . . . The president's time will be filled up with these special envoys.' "

He said he told Poindexter, "If it's so important, then it's going to have to come out of your time," a reference to time allocated for the NSC staff on the president's morning schedule. The visit took place under those conditions, Regan said.

During cross-examination about the Lewis appointment, Regan disclosed that, in his earlier grand jury testimony, he had said Lewis was picked March 14, 1985, as a result of a "consensus" among the senior White House staff.

Regan did not budge from his assertion that Deaver favored Lewis, although the trial was delayed while an FBI agent assigned to the prosecutor's office was dispatched to Regan's Mount Vernon home to pick up copies of memos that Regan said he had used to refresh his memory.

When Regan entered the courtroom to become the 25th prosecution witness, there were none of the friendly glances that Deaver has exchanged with other witnesses, many of whom prosecutors have said are loyal to Deaver and have expressed resentment about being called to speak against him.

Deaver sat expressionless, hands on his face, throughout most of Regan's testimony.

Regan said that the administration had been sharply divided over appointing a special envoy and that then-budget director David A. Stockman had been among the strongest opponents.

Stockman did not support Lewis' selection, Regan said, fearing that he would call for massive spending to end air pollution from U.S. plants along the Canadian border. He said Jack Svahn, head of the president's domestic policy staff, also opposed the appointment.

Before Regan testified, prosecutors questioned Richard Hauser, a former White House lawyer, who said Deaver called him on Feb. 4, 1986, to discuss a General Accounting Office inquiry into the issue, an investigation that Deaver blamed on Rep. John D. Dingell (D-Mich.).

Hauser said he could not recall specifics of the conversation but accurately described the conversation in a memo in which he said Deaver told him that he had "pushed" for Lewis' selection and participated in discussions of the issue at two or three meetings.

Deaver is accused of lying when he told a grand jury that he could not recall being involved in discussion of the issue until March 1985 and that he did not support Lewis.

During the morning session, defense lawyers won from former national security adviser Robert C. McFarlane some qualifications of his testimony Monday that Deaver had supported appointment of the envoy.

McFarlane said Deaver's only interest was in ensuring that a forthcoming summit in 1985 between President Reagan and Canadian Prime Minister Brian Mulroney was a success.

Deaver was not a foreign-policy decisionmaker, McFarlane said. Nonetheless, he said Deaver's role of advising the president how to "portray" his decisions to the public was "probably the most important function in making democracy work."

McFarlane, who left the White House in 1985, provided one of the few moments of humor in the slow-paced trial, which is to resume Thursday.

Asked whether Deaver were paid for helping to prepare for a 1985 Geneva summit with Soviet leader Mikhail Gorbachev, McFarlane said no, then added with the same deadpan monotone that has marked his testimony: "Nobody works for the government to make money."