Sporting a tie from his Mickey Mouse collection and confidently predicting his vindication, former White House aide Lyn Nofziger arrived at the U.S. Courthouse here yesterday for the start of jury selection in his conflict-of-interest trial.

U.S. District Court Judge Thomas A. Flannery estimated that the trial would take three to five weeks once the jurors have been seated. He adjourned yesterday's session after questioning and tentatively seating 18 candidates. He said he wants a pool of 60 potential jurors before opposing lawyers make their cuts.

Nofziger, who left the Reagan White House in 1982 to open a Washington consulting firm, stands accused on four counts of illegal lobbying in violation of the Ethics in Government Act. His partner, Mark A. Bragg, was charged with one count of aiding and abetting.

The charges carry a maximum penalty of two years in prison and a $10,000 fine for each count.

"I think we're going to win this thing," Nofziger told reporters as he entered the courthouse with his wife, Bonnie. "I am innocent of anything and so I assume that a jury, being a typical fair American jury, will find that to be the case."

He was dressed in a blue suit, blue shirt, and a striped tie with his trademark Mickey Mouse emblem.

Independent counsel James C. McKay has a prosecution list of 24 witnesses, including high-ranking White House aides, Secretary of the Army John O. Marsh Jr., former secretary of the Navy John F. Lehman Jr., former chief officials of the Small Business Administration, and the former director of the Office of Management and Budget, David A. Stockman.

Nofziger was indicted for lobbying old colleagues at the White House on four occasions in 1982, twice on behalf of the now bankrupt Wedtech Corp., twice for other clients, Fairchild Industries and the Marine Engineers Beneficial Association.

Federal conflict-of-interest law prohibits former high-ranking government officials from lobbying at their old agencies on certain matters within a year after leaving.

Nofziger has been accused of illegally lobbying then-Counselor to the President Edwin Meese III and Meese's top deputy, James Jenkins, in Wedtech's drive to win a no-bid $32 million Army engine contract. Despite initial resistance from the Army, Wedtech won the contract under the Small Business Administration's set-aside program for minority businesses.

Nofziger said he was sorry he ever agreed to work at the White House after Reagan's election in 1980. "I never did like government," he said. "Now I know why."