D.C. United had looked to this final week of the regular season to shake off last week's disappointing performance at the CONCACAF Champions Cup in Las Vegas and prepare for the Major League Soccer playoffs. But instead of moving forward, United took a giant step back last night with a troubling, 4-2 defeat to the Tampa Bay Mutiny before a season-low 10,846 at RFK Stadium.

The loss halted a club-record 11-game winning streak in league play and prompted serious questions about the readiness of a team that just a week ago seemed prepared to roll to its third MLS title in four years.

"It was an overall poor performance--something we didn't want to see at this particular stage of the season," United Coach Thomas Rongen said, shaking his head in disbelief. "We came out very flat. You can't look at Vegas and say that's the reason why. You can't look at the standings and say that's the reason why.

". . . This is probably something we needed. . . . It's a wake-up call. It makes me certainly believe--and should make the team realize--that we are not invincible."

With the playoffs just 10 days away, United appeared tired and uninspired following its week-long stay at the Champions Cup. For 70 minutes, its forwards were unthreatening, the midfield didn't create much, the defense had several more mystifying letdowns and goalkeeper Tom Presthus, coming off a poor performance last week, didn't exude much confidence.

United (23-8) played well for all of six minutes--just enough time to tie the match after falling behind by two goals. Jeff Agoos and Roy Lassiter struck for goals in rapid succession, but the Mutiny (14-17) responded in the 83rd minute when Musa Shannon collected Carlos Valderrama's pass and blistered an eight-yard angled shot past Presthus.

Forward Manny Lagos, who contributed to Shannon's goal by drawing D.C. defender Carlos Llamosa away from his teammate, closed the scoring five minutes later with a 20-yard blast into the lower right corner.

"We've been giving up too many stupid goals," United forward Jaime Moreno said. "If these things happen again in the playoffs, we won't make it past the first round."

Although there's nothing at stake this week, Rongen was serious about not only winning these games, but playing well with his top players on the field. Instead, he saw one of his club's worst performances of the year.

In the seventh minute, former George Mason University star Ritchie Kotschau sent a long ball over the D.C. defense to Steve Ralston, who chipped a shot over the helpless Presthus for a 1-0 lead. It was the first shot Presthus faced since his rocky outing last Friday against Necaxa of Mexico.

A minute later United should have tied it, but Lassiter shot meekly on a clear run at former D.C. goalie Scott Garlick, who covered the ball easily.

In the 22nd minute, Ralston touched the ball into the box for Lagos, who lifted it toward the far corner. Kotschau got there first from his left back position and slammed the ball into the open side, handing United its first two-goal deficit in a league match in nearly four months.

United evened it on Agoos's 30-yard rocket in the 70th minute and Lassiter's putaway in front of the net following a twice-deflected corner kick in the 76th minute. But D.C.'s defense collapsed again and allowed the Mutiny to attack with minimal resistance.

"We were sluggish out there," midfielder Ben Olsen said. "I don't know what's wrong. We're just not helping each other out."