Teamsters President William J. McCarthy lost a showdown with his general executive board yesterday, triggering threats of a new purge within the top ranks of the union.

In a move engineered by Teamsters Vice President R.V. Durham, a candidate to replace McCarthy in this year's Teamsters elections, the board rejected the nomination of Pennsylvania Teamster Al Barlow, McCarthy's hand-picked candidate for a vacant seat on the board. The vote came at the last day of a three-day board meeting in Palm Springs, Calif.

After the vote, McCarthy threatened to fire Durham from his post as director of national freight negotiations and verbally attacked others on the board who had voted against him, sources said.

"McCarthy's very, very bitter and upset," a source said.

The vote was seen as an attempt by the slate of candidates led by Durham and Weldon Mathis, Teamsters secretary-treasurer, to put some political distance between it and McCarthy.

McCarthy announced last October that, for personal reasons, he would not seek reelection in this year's government supervised elections. McCarthy suffered a stroke early last year and in recent months has been removing people he considers his enemy from the union's top ranks, sources said.

Three of those who were purged -- vice presidents Joseph Trerotola of New York, Walter Shea of Washington, D.C., and Daniel Ligurotis of Chicago -- have filed suit against McCarthy, charging that they were fired from their appointed positions for purely political reasons. All three retain their union vice presidencies.

Union sources said that Barlow, a representative for the eastern conference of Teamsters, was unacceptable to the members of the Durham slate and that they had warned McCarthy in the weeks before the board meeting they would oppose the nomination.

McCarthy refused to back down and insisted Barlow's nomination be brought before the board for a roll-call vote.