The 22nd convention of the International Brotherhood of Teamsters opened here today with videotaped praise from President Reagan and a broadside against government prosecutors and investigators from the Teamsters' indicted president, Roy Lee Williams.

Williams, appointed May 15 as interim president after the death of long-time Teamsters president Frank E. Fitzsimmons, blasted a report from the Senate Permanent Investigations Subcommittee suggesting that he was unfit for office and labeling him a tool of organized crime. Williams told the delegates that the report was "so wrong and so false that I don't intend to dignify it with a response. . . ."

Williams also repeated that his indictment on conspiracy and bribery charges, handed up by a federal grand jury in Chicago last month, was a "damned lie" and would not stop him from fighting for the union's top job.

Earlier, in a videotaped message that drew enthusiastic applause from many of the 2,200 Teamster delegates in the Las Vegas convention center, Reagan urged the delegates to work with him "to revitalize the economy of the nation."

"I hope to be in team with the Teamsters and with all of America's working men and women pulling for a more prosperous American," Reagan said in his message. Earlier in his presentation, the president said: "As a former union president [of the Screen Actor's Guild], nothing makes me prouder than to work together with my union brothers toward a shared goal."

The president appealed for support for his tax cut program, saying that it will help to get the economy "humming" again. "When the economy is humming, it means that your 18-wheelers are humming down the highway," Reagan said to the group. The president was referring to the 19 percent of Teamsters, by union estimate, who are found behind the wheels of trucks. More than four-fifths of the union's 2.3 million members work in hospitals, offices, police departments and service industries.

Neither Reagan nor his White House labor liaison, Robert Bonitati, mentioned in their convention messages today a key issue that had helped bring Reagan the Teamsters' support in the 1980 campaign -- federal deregulation of the trucking industry.The Teamsters supported Reagan's successful White House bid largely because they believed he would support their efforts to overturn or modify the 1980 law deregulating trucking.

As Reagan was giving his address by videotape, about 100 Teamster dissidents outside the convention were protesting Williams' virtually certain elevation of the union's presidency.

The Teamsters' official explanation of the pickets called them an "everchanging cast of union dropouts, college students aimless transients and an elite group of zealots."

"These pickets would not be here without the knee-jerk support supplied by the news media of the country," said Jackie Presser, a vice president and communications director for the international union, who himself has been the subject of news stories about his alleged dealings in organized crime.

The attacks on the media also were included in the numerous eulogies of Fitzsimmons, whose death on May 6 put Williams in position to head the union. "Columinists and reporters wrote of him from their biased perspective on organized labor," said general secretary-treasurer Ray Schoessling of Fitzsimmons. "But the 'infallibility' of the news media notwithstanding, presidents sought his advice.