The Washington Bullets almost blew a 20-point lead yesterday, but-- knowing they would have to face the Philadelphia 76ers in the first round of the playoffs if they lost--regrouped in the final two minutes and defeated the Atlanta Hawks, 99-96.

The victory at Capital Centre enabled the Bullets to finish the regular season with the fifth-best record in the Eastern Conference of the National Basketball Association. The Hawks, who finished one game behind the Bullets in sixth place, will have to play Philadelphia in the playoffs. The Bullets will play the fourth-place New Jersey Nets in a best-of-three series beginning Tuesday at the Meadowlands Arena. The second game will be played here Friday night and a third game, if necessary, will be played at the Meadowlands Sunday afternoon.

The Bullets were 2-4 against the Nets this season, but 0-6 against the 76ers.

"Naturally we wanted to play New Jersey because we haven't beaten Philadelphia yet," said Coach Gene Shue. "We think we can play well against them (the Nets). We're peaking and playing as well as we can right now, but so are they."

Despite their 20-point lead yesterday, the Bullets were not sure they would be playing the Nets until, with three seconds left, Jeff Ruland got a finger on a three-point shot by the Hawks' Eddie Johnson and knocked it off course.

Guard John Lucas, for reasons he wouldn't go into, arrived at the game only minutes before it began, and Shue played him only two minutes. As a result, Frank Johnson went 46 minutes and had 18 points, six assists and three steals. Don Collins also scored 18 points, 16 in the first half, and Shue said he would start the first playoff game even if guard Kevin Grevey has recovered completely from his recent groin injury. Grevey played three minutes yesterday and did not take a shot.

The Bullets had a 90-75 lead with 8:53 to play, but scored only two points in the next six minutes.

Dan Roundfield got the Hawks' last 10 points and they had a chance to send the game into overtime when Rory Sparrow stole a careless cross court pass Greg Ballard intended for Rick Mahorn with eight seconds to play. Sparrow had a breakaway, but the Hawks needed a three-point basket and didn't have any timeouts left. So Sparrow slowed down, let Eddie Johnson catch up and passed to him for the three-point attempt with three seconds left.

It had looked like the game would be a blowout as Collins led the Bullets to a 60-44 halftime lead with an assortment of steals, fast break baskets and wide open, up-tempo style. He had 10 points, four assists and three steals in the first quarter. The Bullets, using a trapping defense that got three steals within 30 seconds, scored 10 straight points at the end of the quarter.

The lead grew to 71-51 on Collins' fast-break basket with 7:10 left in the third period. But the Hawks had cut the lead to 11 by the end of the quarter. Then, after trailing, 90-75, with 8:53 remaining, they made their last run.

Tom McMillen scored five staight points to get them off on a 15-2 spurt that cut the margin to 92-90 with 2:45 to play.

In that span, the Bullets made only one of nine shots and committed three turnovers. The drought ended with Mahorn's 12-foot jump shot that gave Washington a 94-90 lead.

Roundfield and Mahorn traded baskets, but after McMillen missed for Atlanta, Mahorn was fouled by Eddie Johnson and made one of two free throws with 36 seconds remaining for a 97-92 lead. Roundfield and Ruland each made two free throws and Washington led, 99-94, with 17 seconds left. Roundfield scored on an uncontested drive with 13 seconds left.