D.C. United was perfectly content with the results of its previous three games -- unglamorous victories over unimposing opponents to move into a first-place tie in Major League Soccer's Eastern Conference. But the players and coaches were well aware that last night's game against the defending champion Chicago Fire at RFK Stadium would weigh the heaviest on their early-season progress report.

Following a rough start, United sparkled in the second half and pulled away for a 3-1 comeback victory before a crowd of 21,840.

Midfielder Ben Olsen broke a 1-1 tie in the 65th minute and later set up Roy Lassiter's league-leading 11th goal with an elegant cross as undermanned United (7-3) won its fourth straight since losing three in a row.

"We're getting better and we're winning games," Olsen said. "We're slowly starting to play United soccer. . . . We like what we're starting to see."

Chicago (6-4) took an early lead on Jerzy Podbrozny's goal, and the disciplined Fire seemed to settle in comfortably with a flawless defense and an effective counterattack. But United defender Jeff Agoos tied the match late in the first half, thanks to a mistake by Fire goalkeeper Zach Thornton, and D.C. established control with a superb second half.

United also got a well-timed boost from goalkeeper Tom Presthus, who made four marvelous saves -- two on one-on-one situations deep in the penalty area. It also received a courageous performance from the defense, which was without star central defenders Eddie Pope (broken foot) and Carlos Llamosa, who sprained his left knee and ankle Thursday.

"This was a little bit of a test," Coach Thomas Rongen said, "and we showed a lot of pride."

From the start, Chicago tried to exploit United's defensive shortcomings. The strategy worked well throughout the first half as Podbrozny and Josh Wolff found ample space to create dangerous opportunities.

After threatening several times, the Fire broke through on Podbrozny's goal in the 14th minute. Defender Lubos Kubik sent the ball into the middle where D.C.'s Geoff Aunger got his head on it. The ball fell to Podbrozny, who lifted it over a retreating Aunger and back to himself for a clinical volley into the lower left corner.

United enjoyed possession deep in Chicago's end, but tame shooting made things easy for Thornton. Presthus made two good saves in a four-minute span, stopping Wolff in the box and pushing Ante Razov's long, hard bid over the crossbar.

Then in the 39th minute, the highly regarded Thornton handed United the tying goal. With a D.C. free kick just outside the box, Chicago expected D.C. captain Marco Etcheverry to try to swerve one of his precision shots into an upper corner of the net. Instead, he pushed the ball to his right to a charging Agoos, whose 25-yarder slipped through the hands of the leaping Thornton and fell into the net.

In the second half, the pace and intensity built steadily. United had a territorial advantage, but the Fire's counterattacks caused some discomfort.

Then, with about 25 minutes remaining, United struck on a wild sequence. Etcheverry's 35-yard free kick was flicked by Aunger. A Chicago defender headed it straight up. Lassiter's leaping header was miraculously saved by Thornton, but the rebound fell to Olsen, who skipped a shot through a maze of players.

"I just saw commotion coming," Olsen said. "I was waiting for anything. . . . I don't think I could have missed that one."

CAPTION: United's Geoff Aunger, right, battles for the ball with Jerzy Podbrozny, who gave Chicago a 1-0 lead with a goal in the 14th minute at RFK Stadium.