MIAMI BEACH, OCT. 29 -- Like a prodigal son, Teamster President Jackie Presser returned to the House of Labor today, vowing to help build "the greatest political giant this country has ever seen" to fight foes of American trade unions.

The union leader, standing where no other Teamster president has stood for 30 years, told cheering delegates at the AFL-CIO convention that his union's 1.7 million active members would add new muscle to labor's political effort.

The Teamsters voted last week to reaffiliate with the AFL-CIO after a 30-year exile for corruption, and the AFL-CIO Executive Council voted unanimously to readmit the union effective Sunday. The council today created a 36th seat for Presser.

Presser told the convention that the reaffiliation move began two weeks ago when he told AFL-CIO President Lane Kirkland, "Lane, we want to come home.

As Presser concluded his speech to a standing ovation, Kirkland said, "Welcome home."

In voting to allow the Teamsters back into the AFL-CIO, union leaders here have talked repeatedly of the new political and organizing strength the giant union will give the federation.

The Teamsters appear to be counting on the AFL-CIO to use at least part of that new strength to help fight Justice Department efforts to use the federal antiracketeering law to place the union under government trusteeship.

Presser is under indictment on federal fraud charges and is scheduled to stand trial early next year. He also is battling cancer.

In announcing the reaffiliation with the Teamsters last week, Kirkland made it clear that, if Presser is convicted, he would have to resign his Teamsters and AFL-CIO posts immediately. He also made it clear that the Teamsters would be allowed to stay.

Teamster Secretary-Treasurer Weldon Mathis said today that the decision by the AFL-CIO Executive Council last August to fight the Justice Department on the trusteeship issue was a major factor in the reaffiliation request.

The Justice Department threat has become a major rallying point among almost all union leaders here this week.

The central theme of Presser's speech was the need to restore labor's political power to fight just such attacks on organized labor.

Although he did not mention the Justice Department suit in his speech, Presser did refer to it in prepared remarks released by the union. "Something is radically wrong in America when a government wants to impose trusteeships on free and democratic trade unions," Presser said in the prepared remarks.

In his prepared speech, he also referred to the new, more powerful AFL-CIO as a "more durable sanctuary for workers."

Presser told delegates that "there is nobody in America, there is no organization in America, that is stronger today, anywhere in this country than the American Federation of Labor. You represent 15 million people."

To underscore how much power his union would add to the federation, Presser said the Teamsters collected $1 a week from 500,000 members for political action.

"Now, that may not seem like much," he said, "but, when you have 500,000 people paying $1 a week, you have an awful lot of money to spend. And without money you're going nowhere in the political arena in this country."

Although Presser rambled, was occasionally incoherent in his speech and ignored his prepared text, no one in the cavernous hall seemed to mind. Teamster officials said he has been undergoing radiation treatment for lung cancer.

By simply appearing, Presser was a message of unity and power for a labor movement that considers itself under siege politically and economically.

Before his appearance, Teamster Executive Council members were clearly among the convention's stars as they were mobbed by well-wishers from the rank and file and international union presidents.

Throughout his appearance, Presser wore a baseball cap emblazoned with the AFL-CIO emblem to hide the fact that he has lost his hair. A tumor was removed from Presser's lung last January, but Teamster officials insisted that he is doing well and that any problems today were the result of radiation treatments.