D.C. United had no excuses last night. No long trips from which to recover. No starters sidelined by injuries. Nothing to prevent the club from rediscovering the form that had produced the best record in Major League Soccer.

But in its final rehearsal before the playoffs, United came up with another uninspiring performance and lost in a shootout to the desperate New England Revolution, 2-1, before 20,695 at RFK Stadium.

"We certainly wanted to finish the season on a little different note than we did," Coach Thomas Rongen said. "We played very poor. . . . We've got a week to regroup. There's no reason for us to panic at this particular time."

United (23-9, 57 points) will open the Eastern Conference playoffs Saturday night at home against the fourth-place Miami Fusion (13-19, 29), which sealed the final postseason berth with a 2-0 victory over Colorado last night. There were a couple of scenarios in which the fifth-place Revolution (12-20, 26 points) could have squeezed ahead of the Fusion, but most involved Miami losing.

To compound its problems, United lost central defender Carlos Llamosa in the 69th minute with a sprained medial collateral ligament in his right knee. Llamosa, an all-star who missed several games with a quadriceps injury this year, will be re-examined today.

"We're pretty concerned," trainer Rick Guter said. "There is some indication it could be serious, but we'll know more in the next 24 to 36 hours. Right now, all we can do is wait."

Said Llamosa, who was injured on Joe-Max Moore's slide tackle near midfield: "It's sore, very sore. I don't know what's going to happen."

United's recent problems began at the CONCACAF Champions Cup in Las Vegas with three sluggish outings, resurfaced Wednesday night during an embarrassing 4-2 home loss to Tampa Bay and continued for most of last night's game.

Its defense showed improvement and goalkeeper Tom Presthus rebounded from a rough couple of games with two sparkling saves, but the attack sputtered again. United's only score came in the second minute on an own goal, and the club finished the first half with one shot. It created several opportunities in the second half, but poor decision-making and wayward shooting let the match drift into a shootout, which the Revolution won by a 3-2 score.

Things started very well for United. Ben Olsen dashed down the left flank and was knocked down by Mike Burns. Marco Etcheverry took the free kick from just outside the penalty area, serving the ball into the six-yard box. Sensing pressure, Revolution defender Ted Chronopoulos tried to chest the ball down to goalkeeper Jeff Causey just a few steps away, but instead sent it into the right side of the net after just 90 seconds.

United didn't do much else the remainder of the half and allowed the equalizer five minutes after intermission. Former United captain John Harkes, making his first appearance against his former team since being traded last January, swung a one-hop cross into the center of the penalty area, where Moore blistered a 13-yard shot into the right side for his 15th goal of the year.

United's attack was much smoother the rest of the way, but Burns cleared Carey Talley's header off the goal line and D.C. forwards Roy Lassiter, MLS's leading goal scorer, and A.J. Wood just missed several other chances.

"Roy's job is to finish goals, and Roy knows that," Rongen said. "Roy needs to put those balls away. It's very simple."

Lassiter could have won it in the 86th minute, but headed Etcheverry's long, high cross off the mark from close range.

"We'll be ready for the playoffs," Wood said. "This team has a knack for rising to the occasion and stepping up its play. I'm not worried."

United Notes: Forward Jaime Moreno served a one-game suspension for an accumulation of yellow cards. . . . Last night's attendance lifted D.C.'s final average to 17,419, third highest in the league behind Los Angeles and Columbus. Last year D.C. averaged 16,008, fifth best in MLS. . . . The club announced that NewsChannel 8 will show Saturday's playoff opener live.

FUSION 2, RAPIDS 0: Eric Wynalda and Welton scored early in the second half as Miami clinched the final playoff spot in the East by defeating playoff-bound Colorado (20-12) in Fort Lauderdale, Fla.

GALAXY 1, WIZARDS 0: Visiting Los Angeles (20-12) clinched first place in the Western Conference on a 25th-minute goal by Ezra Hendrickson. Kansas City finished 8-24.