Teamsters union officials staged a huge pep rally here yesterday to help improve their image with the union's 2 million members.

But what the world saw and heard were grim-faced sergeants-at-arms blocking the entrances, dissidents picketing outside and reports of a rank-and-file complaint seeking the ouster of Teamster President Frank Fitzsimmon

No one got a chance to see what was later described as a resounding, unanimous vote of confidence from the 2,000 participants for Fitzsimmons and other union leaders inside the closed doors of the meeting room at the Washington Hilton Hotel. Nor did people see what participants defense against media criticism and government attacks.

Instead they saw pickets outside the hotel carrying signs reading "Clean Up Your Act" and "Throw the bums Out."

Seeking to upstage the meeting even before it started, three rank-and-file members affiliated with PROD, a dissident organization of Teamsters members, went to the union's Washington headquarters to file charges aimed at Fitzsimmons' removal.

The charges - alleging misuse of union funds, nepotism and hiring of "disreputable individuals" with organized crime connections - were dismissed by a Teamsters spokesman as a publicity gimmick.

Fitzsimmons declined to discuss the charges with reporters as he entered the meeting, but issued two statements, immediately before and after the three-hour session, assailing press coverage of the union.

In the statements, Fitzsimmons, who took over as Teamsters president in 1971, also adamantly denied speculation that he may resign and said he will be a candidate for re-election at the union's next convention in 1981.

The meeting, which was arranged amid tight secrecy over its purpose, was called to clarify what officials described as "confusion" among rank-and-file members over grand jury investigations, charges by union dissidents, unfavorable publicity and government action to remove Fitzsimmons and other union officials as trustees of the union's largest pension fund.

Invitations went out to all 800 Teamsters locals, and about 2,000 of roughly 7,500 union officials from the United States and Canada attended, according to a union spokesman.

One participant said most of the decision at the meeting was devoted to assurances that the pension fund was sound. He said the government's action to oust Fitzsimmons and other union pension fund trustees was described by union officers as the first step toward a government bid to take control of all union pension funds.

In another statement, the union charged that the labor movement as a whole is experiencing "an assault from outside sources seeking to capture labor for a political power base" and said this was one reason for the meeting.

"So while many would like to make much of our meeting today, Insinuating much and implying more," Fitzsimmons said. "we view our meeting as nothing more than an exercise of our responsibilities as good trade unionists.

The charges against Fitzsimmons, which will bw considered by the union's executive board, allege that the union's president has authorized favored colleagues to hold multiple job, approvad "sweetheart contracts," collaborated with racketeers, passed on work to his sons and failed to take action against "pilfering" of trust funds.

The charges were filed by Peter Vitiano by Jersey City, N.S., John Catlett of Lanham, Md., and William Berryhill of Hagerstown, Md.

Another dissident group, Teamsters for a Democratic Union, issued a statement challenging Teamster leaders to a televised debate, to hold a referendum on their stewardship, to open union publications to dissident voices and to act to curb intra-union violence.