Long after disconsolate American fans had filed out of Murdock Stadium on the El Camino College campus today, the drums and cowbells were still beating out their rhythms in the stands.

Several hundred supporters of Trinidad and Tobago continued to celebrate the last-gasp goal by the midfielder Hutson Charles that earned the Caribbean island nation a 1-1 tie with the United States in World Cup qualifying play.

The goal, in the 88th minute, cost the United States a valuable point in its effort to reach next year's World Cup in Italy. The road ahead can only be more difficult now for the Americans, the first team in the five-nation group not to win a home match.

Costa Rica Leads Standing

Costa Rica leads the standing with a 2-2 record and 4 points. The United States has a 1-1-1 record and 3 points. Guatemala is 1-1 with 2 points, and Trinidad and Tobago's tie in its opening match today gives it 1 point. The fifth team in the group, El Salvador, has yet to play. Only the top two teams in the final standing will go to Italy.

It appeared that the United States was sure to take both points, but a lapse in the closing minutes cost it dearly. An excellent fake by Marlon Morris left two American defenders stranded, and when the ball reached Morris, he had only the goalkeeper, David Vanole, to beat.

Vanole had no chance.

To that point, the United States had clung tenaciously to the 1-0 lead it had been given in the 48 minutes by Steve Trittschuh.

The United States goal was set up by Tab Ramos, easily the most skilled of the American players. He controlled a pass sent to him, then floated the ball into the goalmouth, where Trittschuh trapped it with his chest, turned and fired it into the roof of the Trinidad net from close range.

Caught Flat-Footed

The Trinidad players were caught flat-footed on the play, apparently expecting an offside call, which never came. Referee Luigi Agnolin of Italy had no hesitation in pointing to the center spot, indicating that the goal would stand.

To most of the crowd of 10,000, that was the high point of the match, played under cloudy skies. The field was hard and bumpy and the grass needed cutting.

But the United States had only itself to blame for not putting the game away early. The midfielder Bruce Murray, for one, missed an easy shot in the first half.

That happened in the 32d minute, when a crossing pass from the American midfielder, John Harkes, to the right of the Trinidad and Tobago net eluded the visitors' defense, including the goalkeeper Earl Carter, and found Murray unguarded at the far post.

American Fans Groan

Murray had the simple task of sidefooting the ball into the open net, but somehow contrived to steer it wide, to the groans of the American fans.

Those groans were even louder when Charles tied the score in the dying minutes.

''I can't explain it,'' said the United States coach, Bob Gansler. ''I guess we think that after we score we have it won, and we let up.''