The afternoon was ripe for heartbreak. Again.

Late in the fourth quarter the Federals led, 28-21, but Los Angeles was driving, and everyone in RFK Stadium knew the likely scenario: a late touchdown and a two-point conversion. Or maybe a last-second hurricane. Somehow disaster would strike, and it would be the Federals applying for relief.

The Express had the ball on the Washington 38. Fourth down. As he dropped back to pass, quarterback Mike Rae seemed to have at least one receiver open for the necessary yardage. But then, like a freshly thawed mastodon, 40-year-old Coy Bacon started chasing Rae out of the pocket. For a moment Rae appeared free of peril, but Bacon dove, stuck out his mitt and tripped Rae for a sack, and the Federals (3-14) had their second victory in three games.

"It was one of those shoestring jobs," Bacon said. "One of those 1968 moves."

Only 9,792 watched the team's next-to-last game of the inaugural U.S. Football League season; there were 12,160 no-shows. Before Bacon's sack, the absentees also had missed Craig James scoring what indeed turned out to be the winning touchdown, on an 18-yard run with 6:28 left.

"We finally finished a game," said James, who himself completed the day with 90 yards and two touchdowns on 14 carries.

The Express lost its chance for a playoff spot when Oakland beat Boston, 17-16, Saturday night for the Pacific Division title. Los Angeles (7-10) beat Washington, 20-3, in the second week of the season, and in the first half yesterday appeared headed for a similar result.

"The fact that we were eliminated from the playoff last night, I don't think that hurt us," said Coach Hugh Campbell.

The game began poorly for Washington, especially for James. Early in the first quarter, he started an 11-yard run from his 15, but he advertised rather than carried the ball and Los Angeles forced the fumble, recovering on the Washington eight. Three plays later, John Barnett ran one yard for the touchdown.

Former UCLA star Tom Ramsey started at quarterback for Los Angeles. He threw to Anthony Allen for a 40-yard gain and closed an 81-yard drive by scoring on a keeper from one yard, making it 14-0 with 14:49 left in the second quarter.

"It's the same pattern," Washington owner Berl Bernhard would say later. "We get behind and then we stay tough and come back."

The comeback began with a defensive break. Safety Doug Greene, second in the league in interceptions, got his ninth on the Express 42 and returned it to the 25.

Quarterback Kim McQuilken, who had begun the game erratically, connected on a 20-yard pass to Billy Taylor. Next play, Taylor ran three yards and it was 14-7 with 13:15 left in the half.

The Federals had an excellent chance to tie before intermission but wide receiver Mike Harris literally dropped the opportunity. With the ball on the Los Angeles 30, and 1:18 remaining in the half, McQuilken threw deep to Harris, open on the goal line.

"I just plain dropped it," Harris said. "I'm telling you, I wasn't exactly having one of my best days. Los Angeles traded me right after they beat Washington the first time, so I was keyed up. I wanted to do something to get back in it."

Harris would get his chance.

The Washington defense, led by Ron Estay, Bennie Smith and Tony Suber, denied the Express a score early in the third quarter after Federals receiver Charles Chisley had fumbled on the L.A. 36. Ramsey left with a sprained ankle on the last play of the first half, but substitute Rae was the very quarterback who played so well against Washington three months ago.

The defense, however, forced a punt, and Eric Robinson returned 25 yards to the Los Angeles 40.

Coach Ray Jauch had benched James after his early fumble, but the rookie running back returned to carry 31 yards on the drive, including a five-yard scoring run midway in the third period.

"The coach wanted me to get my mind right," said James, who was in the special teams lineup during the second period. Jauch claimed James had hurt his ankle.

McQuilken, who completed 17 of 26 passes for 183 yards, led the Federals on a 90-yard drive to a 21-14 lead. A roughing-the-passer call helped, as did the running of Taylor, James and Curtis Bledsoe. McQuilken, with third and 18 from the Los Angeles 32 and nine seconds left in the third quarter, threw to Harris.

Touchdown. "Thank God I caught it," Harris said.

Bernhard doffed an Elizabethan hat in the owner's box and thrust his fist in the air.

The Express tied the game on its next possession. Rae threw passes to LaRue Harrington, who gained 105 yards rushing, Allen and Wilbert Haslip to set up Tony Boddie's six-yard scoring run with 10 1/2 minutes to play.

Washington followed with its winning drive. After a 19-yard pass to Harris and a crucial eight-yard completion on third down to Taylor, McQuilken pitched to James and he made the winning 18-yard run.