This was supposed to be the year, the series and the opponent that would end D.C. United's three-year grip on Major League Soccer's Eastern Conference. But with a stirring performance that had a raucous crowd of 21,451 singing and dancing into the cool evening, United routed the Columbus Crew, 4-0, yesterday at RFK Stadium to win a tense, best-of-three conference series and secure its fourth consecutive trip to the championship game.

Captain Marco Etcheverry assisted on the first three goals and scored the last, a 23-yard free kick into the upper left corner that set off a wild celebration with about four minutes remaining.

Forward Roy Lassiter, who had been in a scoring slump for about four months, had two goals, including a spectacular bicycle kick early in the second half.

Said goalkeeper Tom Presthus: "We played such a perfect game."

The victory sent United (27-10) to next Sunday's final against the Western champion Los Angeles Galaxy (24-13) at Foxboro (Mass.) Stadium--a rematch of the 1996 final won by D.C. in sudden-death overtime at the same location.

United has won the conference title in each year since the league was formed in 1996, but this season was its greatest challenge. The confident Crew (22-15) forced a decisive third game with a 5-1 rout last weekend in Game 2, and there were questions whether a shaken United squad would be able to regroup.

"We responded the way good teams do: We let football do the talking," Coach Thomas Rongen said.

United's defense yielded few opportunities to a high-powered Crew attack, and until the 89th minute, Presthus had more assists (one) than saves (none). Meanwhile, United surged forward with every touch of the ball, with Etcheverry's inspired play leading the way. It was Columbus's 13th consecutive loss at RFK and increased United's all-time playoff record at home to 12-0.

"D.C. did exactly what they had to do at home, they did exactly what they've done for the last 13 games" against Columbus, Crew Coach Tom Fitzgerald said. "Some day we'll break that string."

Following last weekend's rough game, yesterday's match began as expected with physical play and some deliberate fouling. Etcheverry was assessed a yellow card for tripping and Columbus's Robert Warzycha also was cautioned for dumping Etcheverry from behind.

But once things settled down, United got into a rhythm. Its pressure paid off in the 17th minute on an exquisite sequence. Carey Talley's cross was deflected to forward Jaime Moreno, who settled the ball with his chest at the top of the penalty area and then touched it to Etcheverry. Moreno darted into the box and received Etcheverry's pass in stride before slipping a 12-yard shot past goalkeeper Mark Dougherty.

United's impassioned play didn't let up, and following a couple of threats, D.C. went up by two goals following another pinpoint pass by Etcheverry. This time the sequence began with Presthus distributing the ball to Etcheverry, who lifted a 30-yard pass over Lassiter and defender Mike Lapper.

The chase ended with the fleet Lassiter gaining position and nodding the ball into the box. Dougherty held his ground, but couldn't stop Lassiter's left-footed shot that nestled inside the far corner.

United increased the lead to 3-0 in the 52nd minute on an eye-catching goal by Lassiter. Etcheverry lifted the ball to a back-pedaling Moreno, who headed it into the middle of the box. The unmarked Lassiter was a little ahead of the play, so he leaped and whipped his left leg over his head for a six-yard finish past the stunned Dougherty.

Lassiter bounced back up and charged toward the aghast spectators behind the goal, his eyes agape, his arms pumping with excitement before his ecstatic teammates reached him.

"That was the real D.C. United," Moreno said. "When D.C. United plays like that, no one can stop us. It's a great feeling."

United Notes: Many fans were unable to get into the stadium until nearly halftime because of long lines at will-call and ticket windows. . . . Midfielder Thomas Dooley didn't accompany the Crew here in order to attend a coaching clinic in his native Germany. He has been unhappy about his lack of playing time this season and wasn't expected to be one of the eligible substitutes yesterday. . . . D.C. defender Diego Sonora (calf injury) was initially included in the starting lineup, but scratched just before kickoff.