Even as he was being prosecuted on criminal charges, Teamsters union President Roy Lee Williams continued to hobnob with top administration officials, including President Reagan.

His was the only major labor organization that backed Reagan's presidential candidacy.

With his conviction yesterday for bribery conspiracy, the leader of 2 million truckers and others in the union, including the wearer of the Mickey Mouse suit at Disney World, secured his place in a colorful tradition.

A succession of officials of the nation's largest labor union and its multibillion-dollar Central States Pension Fund have showed a penchant for maintaining their powerful union positions despite criminal convictions and documented involvement with organized crime.

Williams, 67, a beefy former trucker known for his swagger and expletive-deleted language, has been indicted twice on embezzlement charges, in 1962 and 1972, and once on charges of making false entries in government reporting forms. He was acquitted in the first two cases, and the other was dismissed.

He started his career driving a truck in 1935 and rose through the ranks. On May 15, 1981, as Teamsters president Frank E. Fitzsimmons was dying of cancer, the union's general executive board anointed Williams as successor.

Despite an 11-count indictment hanging over him, delegates at the International Brotherhood of Teamsters convention in Las Vegas in June, 1981, gave him an overwhelming vote of support over the objections of a small dissident group. They also raised his salary by 40 percent, to $225,000 a year.

Williams declared on the convention floor: "No indictment will stop me!" He has consistently called the charges "a damned lie."

Asked shortly before the convention in a television interview if he was a "crook," he replied:

"I don't think I am. I know Roy Williams better than anybody, and I've done a good job and I went through all kinds of trials and tribulations and the government hasn't proved anything on me."

In 1980, he took the Fifth Amendment two dozen times before a Senate subcommittee hearing on his dealings with organized crime figures in Kansas City, Mo.

As recently as last July, more than a year after his indictment on the latest charges, he met with Vice President Bush at Teamsters headquarters. Last February, after meeting with Williams at the White House, Reagan praised his "statesmanlike" negotiating style, according to an official at the meeting.

Williams' conviction comes as an anti-racketeering bill spearheaded by Sen. Sam Nunn (D-Ga.) awaits House action after Senate approval. The bill would prohibit convicted felons from serving as officers of labor groups or their pension plans.

It would apply retroactively to Williams and force him to vacate office immediately, an aide to the Senate's permanent subcommittee on investigations said yesterday. It would apply at time of conviction, while under existing laws, officials can remain in office through the appeals process.

Nunn said yesterday that the legislation was designed for cases such as that involving Williams. "It is a real indictment of our union process for someone convicted of a felony to retain these positions sometimes for years and years" and undermines the judicial system, he said.

Such positions, he noted, involve great power and fiduciary trust and can affect "thousands of working people and the overall economy. . . . "

Labor Secretary Raymond J. Donovan and AFL-CIO President Lane Kirkland have testified in support of the bill, although Kirkland has expressed reservations. The Teamsters have lobbied against it.

Other Teamsters presidents who served time in prison include the late Dave Beck and James R. Hoffa, who disappeared under mysterious and, authorities surmise, violent circumstances in July, 1975. Last week, he was declared legally dead.

The Teamsters' $3.5 billion pension fund has been plagued with allegations of widespread abuse and, under an agreement negotiated with the government, has been placed under independent management.

The late George Meany kicked the union out of the AFL-CIO in 1957 because of allegations of corrupt practices, and there have been hints recently that reaffiliation plans may be under way. AFL-CIO officials had no comment yesterday on Williams' conviction.