There were plenty of happy folks at RFK Stadium last night after D.C. United's sixth consecutive victory, an entertaining 3-1 triumph over the Miami Fusion.

Coach Thomas Rongen was ecstatic about the electrifying first-half performance by forward-turned-midfielder Jaime Moreno. Defender Eddie Pope was thrilled to return from a six-week layoff after breaking his right foot. Forward Roy Lassiter was tickled to score his Major League Soccer-best 12th goal on an early strike.

And among the 12,136 spectators, U.S. men's national team coach Bruce Arena probably had the widest smile. Three days before the United States will face world power Argentina here, Arena watched four of his players -- three from United and one from the Fusion -- come away without more than a few bumps and bruises.

United defender Jeff Agoos, a probable starter at left back for Arena, played a half before being replaced by Pope. Midfielder Richie Williams, a reserve against Argentina, had an exceptional 79 minutes, setting up the second goal by Ben Olsen and scoring the third on an acrobatic shot. Lassiter, a likely second-half substitute on Sunday, went the distance and shook off a nasty head-to-head collision in the first half.

Miami defender Leo Cullen, a U.S. reserve, also played the entire game.

"I didn't feel like I got much of a workout," Agoos said. "Miami ran me a little bit, but I feel good. I won't have a problem playing this weekend. It was a nice evening of soccer."

It was nice for all of United (9-3, 23 points), which extended its Eastern Conference lead to eight points over idle Columbus. On Sunday, while the U.S. squad plays the Argentines, short-handed United will go on the road to face the Crew (7-4). While Rongen won't have his top Americans, he will get back captain Marco Etcheverry, who was suspended from last night's game for accumulating yellow cards.

With Moreno running the show, United went ahead in the eighth minute on Lassiter's goal. Diego Sonora got it started with a delivery into the box to Geoff Aunger, who nodded it forward. The ball skipped off the forearm of Aunger's defender, Arley Palacios, and bounced to Lassiter for a one-touch finish from six yards.

Following four more serious threats, United doubled the lead on an exquisite play in the 32nd minute. Moreno touched the ball back to Williams, who presented a soft pass to the angling Olsen in the box. In one graceful move, Olsen met the ball and smacked a left-footed shot just inside the right post.

With a seemingly comfortable lead at the half, Rongen replaced Agoos with Pope. "My foot held up pretty well," Pope said, "but I'm tired. It will take some time to get back in shape."

Miami Coach Ivo Wortmann shook up his team with three substitutions at halftime. The moves had an impact, as the Fusion attacked with more vigor. Welton hit the crossbar and United had to reorganize before it got into trouble.

But Williams expanded the lead in the 58th minute, gathering Palacios's poor touch and somehow getting off a shot as Palacios pulled him to the turf. If Williams hadn't lifted the ball over reserve goalie Garth Lagerwey for his second goal of the year, referee Noel Kenny certainly would have been justified in awarding a penalty kick.

The Fusion (4-10, 8 points) scored in the 69th minute. Henry Gutierrez ran onto Pablo Mastroeni's cross and headed it in from short range, ending goalkeeper Tom Presthus's scoreless streak at 235 minutes.

Soccer Notes: Prior to the MLS game, the Northern Virginia Royals were eliminated from the U.S. Open Cup with a 5-3 first-round loss to the amateur Cocoa (Fla.) Expos. Cocoa tore through the Royals for a 4-1 halftime lead. Tim Prisco, Alberto Ogando and Rick Engelfried scored for Northern Virginia, which is United's third-division minor league affiliate. . . .

MLS announced that the second half of its All-Star Game doubleheader July 18 in San Diego will have Chivas of Guadalajara, Mexico's most popular club, facing Chilean power Universidad Catolica.

Miami 011D.C. United 213

SCORING -- M: Gutierrez (Welton, Mastroeni), 69th minute; D.C.: Lassiter (Sonora, Aunger), 8th; Olsen (Moreno, Williams), 32nd; Williams (unassisted), 58th.

LINEUPS -- M: Cassar (Lagerwey 46th); Mastroeni, Cullen, Palacios; Maessner, Rooney (Gori 74th), Gutierrez, Rocha (Aldrich 46th), Kozic (Kozic 46th); Welton, Serna; D.C.: Presthus; Sonora, Agoos (Pope 46th), Kamler; Williams (Talley 79th), Aunger, Olsen, Moore (Otero 68th), Moreno; Wood, Lassiter.

CAPTION: Ben Olsen, left, battles Fusion's Alen Kozic at RFK. Olsen, Roy Lassiter and Richie Williams scored goals for first-place United, which improved to 9-3.