Boston quarterback Johnnie Walton threw a 39-yard touchdown pass to Charlie Smith with 7:07 left to play and the Washington Federals lost to the Breakers, 21-14, before 7,303 fans awash in rain and unfulfilled promises yesterday at RFK Stadium.

Although a barrage of advertisements during the week promised otherwise, there were no suntans available at RFK. And the Federals, now 1-11, could not avoid another disheartening loss, their eighth straight. There were 14,406 no-shows, making the crowd the smallest of the U.S. Football League season at the stadium.

"We've had rain on each Sunday we have played," said Federals owner Berl Bernhard. "Combine that with our record and you can't blame people for staying away."

Adding to the Federals' loss, running back Eric Robinson, the USFL's leading kick returner, suffered a fractured sternum and is expected to be out for the season. He was hit trying to make a tackle in the second quarter on a return by the Breakers. Robinson had been averaging 30.6 yards on 14 returns.

The winning touchdown came two plays after linebacker Mike Brewington intercepted Mike Hohensee's pass. "It's really simple," said Federals Coach Ray Jauch. "They moved when they had to move. And we didn't stop them when we had to stop them."

Walton, 35, who played in the National Football League and the World Football League and came out of retirement at the beginning of this season, had 27 completions in 46 passes for 326 yards and two touchdowns. "Walton reads defenses very well," said Boston Coach Dick Coury. "He is dangerous on the attack. Considering the conditions, he threw very controlled passes and kept the team very relaxed on the field."

Maybe too relaxed. A play before throwing the winning touchdown pass, Walton set up behind his offensive guard and was calling signals before Jerrell Franklin, waving his quarterback's hands away from his rump like an old cow swatting flies, managed to get Walton behind his center. "I forgot my area of responsibility," Walton said.

The next play, Walton found Smith 10 steps behind defensive back Willie Holley. On the extra point, the Breakers went for two. Walton threw a swing pass to running back Dennis Johnson, trailing a wall of blockers, and he scored without being touched.

"They didn't seem like a 1-11 team," said Walton, a former coach at Elizabeth City College, his alma mater.

"Their defense has a lot of experience. If they stick together, they'll be a team to deal with in the future."

The only player the Breakers had trouble dealing with was running back Billy Taylor, who gained a team record 104 yards on 13 carries. Taylor, waived by Boston at the beginning of the season, also caught four passes for 73 yards and one touchdown.

"How long can I keep motivating myself?" Taylor said. "It's been terrible playing in this slump the last eight weeks. I know we have the players. I know we can compete with any club in this league. We just never pull it out in the clutch.

"It all comes down to who wins and who loses. If we don't win, it doesn't matter how many yards I gain."

Boston kicker Tim Mazzetti, the league's leading scorer, was good on field goals tries of 19 and 27 yards in the third quarter to cut the Federals' lead to 14-13.

Brewington made the game-turning interception midway through the fourth quarter. He caught the ball at the Federals' 44 and returned it 10 yards. Two plays later, Walton passed to Smith.

The Federals had the ball once more but failed to get past their 40. They punted with 4:33 remaining and Boston ran out the clock. Walton's seven-yard pass to Dennis Johnson on third and six helped them keep the ball.

For the Federals, Hohensee completed 15 of 27 passes for 226 yards and two touchdowns. It was the first time this season he had started consecutive games.

Boston scored on its first possession, using 9:04 to drive 72 yards on 15 plays. Walton passed to wide receiver Frank Lockett for a 14-yard touchdown and Mazzetti's extra point made it 7-0.

A steady rain forced most of the anguished fans under the mezzanine overhang, where their early disgust could be heard in boos and feverish heckling. Things looked ugly. Sloppy, disheveled turf, raincoats, heartless defense--Federals' weather.

The Breakers controlled the ball in the first quarter, using up 12 1/2 of the 15 minutes with a mixture of runs and passes. Their defense, led by free safety Joe Restic and Brewington, shut down the Federals, whose only promising moment came on a 24-yard run by Taylor.

Taylor scored the Federals' first touchdown on their third possession, with 5:54 remaining in the half. Hohensee dumped a wobbly screen pass to him on the strong-side hash mark and, after breaking two arm tackles, he high-stepped the last 10 yards of his 46-yard run to the end zone.

Mike Holmes put the Federals ahead, 14-7, with a touchdown on a 34-yard pass from Hohensee with two minutes left in the second period. Catching the ball at the hash mark, he outran the defense to the goal line.

After Sandro Vitiello kicked the extra point there was a sudden celebration in the rain. Fans crawled out from their bowers; an assortment of raincoats and umbrellas appeared suddenly. Even with the ugly skies, there was a hint of sunlight.

But once again, the Federals could not hold the lead, and the odious losing streak went on.