Paul Cannell rammed home three goals, the last with 2:57 left in a second sudden-death overtime period, to rally the Washington Diplomats to a dramatic, but costly, 3-2 triumph over the New England Tea Men yesterday at RFK Stadium.

Washington lost leading scorer Alan Green with a groin pull before the North American Soccer League game, watched by 11,450 despite a heavy rain, was six minutes old. Green, who has 21 points this season, said he probably would be out at least a month.

Green's injury, the Tea Men's 2-0 lead at intermission and the game-long downpour that turned the field into a swamp boded ill for the Diplomats' chances of averting defeat.

But Cannell, making his first start in three games since breaking his cheekbone, virtually carried his team singlehandedly to victory in the second half.

The triumph gave the Dips a 9-3 record and kept them a close second in the National Conference Eastern Division, eight points behind the Cosmos (10-2), who beat Toronto, 3-1, yesterday.

Cannell's game-winner, a five-yard kick following passes from Sakib Viteskic and Rene Breevoort, caught the Tea Men defense flatfooted. In fact, several New England players felt the goal should have been disallowed because Cannell was offside.

"We played for it (the offside) but didn't get it," said goalkeeper Kevin Keelan. "I thought it was (offside), but the referee gave no signal."

Cannell said he didn't know whether he was offside or not.

"I've always been taught to play the ball, put it in the net and argue later," said Cannell, who has six goals on the season. "When I scored, I didn't see any signal so I figured it was good. Maybe I was offside by eight or nine yards. Anyway, I get paid to score goals, that's my job."

Cannell earned his money yesterday. When Green limped off, the Washington offense bogged down, in part because of a large muddy area 25 yards from the goal area that played better defense that any human ever could. Any ball shot through the area stopped dead and players on both teams would go sliding by.

Cannell had fewer problems with the slop. He merely stayed in the middle of the goal area and waited for the ball to come his way.

New England gained a 2-0 advantage on goals by Keita, who took advantage of errors by defender Don Droege and goalie Bill Irwin to score.

"We gave them away trying to put pressure on at the other end," said Washington Coach Gordon Bradley. "They gave us a lot of problems but nothing we couldn't correct. We made one or two tactical changes the second half and they worked."

One thing Washington did was slow the ball and work for shots. Viteskic, Sonny Askew and Joe Horvath worked the ball inside and began looking for Cannell. His first goal came at the 60:06 mark as Aske w sent the striker a perfect cross and Cannell headed the ball past Keelan.

New England, which was outshot, 25-8, had all but stopped trying to score and attempted to hang on for dear life. Washington, hoping to stay close to the Cosmos, was not about to allow a stall. The Dips began pressing on defense and firing shot after shot at Keelan.

"I expected them to come at me," said Keelan, who had four saves. "Being behind, they had no choice."

Cannell's second goal was stunning. Tommy O'Hara lofted a free kick toward the New England goal, where Horvath leaped up and headed a shot right at Keelan. The 37-year-old former English star managed to get a hand on the ball and punch it out, but Cannell left his feet and sent a diving header right back past Keelan to tie the score at 2-2 with 11:26 to play in regulation.

New England held on and forced the overtime. Washington dominated the first 7 1/2-minute session, but Keelan and defenders Artur and Chris Turner made several nice plays to stymie Washington that period.

The second session was uneventful until Cannell slipped in the game winner. It was only the third three-goal game for a player in Washington history.

"It was just a matter of being in the right place," said Cannell. "All I need is a step on my defender and I'll get the ball. The people in the stands were great out there in the rain and they made me want to play."

Washington starts a three-game road trip Wednesday in Toronto. CAPTION: Picture, Paul Cannell (9, in dark uniform) falls over goalie Kevin Keelan while scoring second goal. By Larry Morris - The Washington Post