When Philadelphia Coach Matt Guokas and his 76ers decided at halftime last night that they had to do something about the shooting of Gus Williams and Jeff Malone, perhaps nobody in the visitors' locker room expected the drastic turn of events that was largely responsible for their Game 3 playoff victory over the Bullets at Capital Centre.

After hitting nine of his first 12 shots and scoring 21 points midway through the third quarter, Williams went 20 minutes without a field goal. And Malone, the team's leading scorer, was held scoreless for roughly the same period.

The Bullets guards said they went cold. "Something went wrong, but I'm still not sure what it is," Malone said.

But the 76ers figured they had a little better handle on what happened. Sedale Threatt happened to Williams. Julius Erving happened to Malone. Threatt and Erving also had help.

With foul-troubled Cliff Robinson on the bench much of the game, stopping Williams and Malone meant the Bullets, pretty much, were done.

Erving said Washington's offense is "very predictable. They just run hot and cold. When they're hot, they're tough to stop. When they're not, you have to take advantage of it."

But Erving and Threatt did a lot to make sure the Bullets guards went cold and stayed that way.

Erving blocked six shots. And as Guokas said, "Sedale did an outstanding job defensively. Gus had a tremendous first half and he started to have a great third quarter."

Guokas had planned for Threatt to play no more than four minutes at point guard, to give all-star Maurice Cheeks a rest. But at the end of the game, in the prime-time minutes, there was Threatt still on the floor in Williams' face, making sure the Bullets veteran didn't go on a seven-for-nine shooting tear like the one he used to start the game.

"Early in the game, Gus ran off a lot of picks," Threatt said. "We decided we had to make him run to the base line and double-team him. Clemon Johnson helped me trap him on the base line, and we tried to make him throw the ball back out."

Erving said he knew from the beginning what was necessary to keep Malone from hitting his average, 21.8 points. "Keep the ball out of his hands as much as possible," the Doc said.

With Malone making only six of 16 field goal attempts, Erving recalled something else. "When they go away from him, they really go away," Erving said. "So I could roam around and help out in other situations."

Several of those situations produced blocked shots for Erving, who hadn't been proud of his playoff performances to date. "My shots had been getting blocked," Erving said, "so I may as well block somebody else's shots."

Threatt didn't register any blocks. But the 76ers felt he stayed in Williams' way enough the second half. "He was really active, defensively," Johnson said. "But this is the NBA, and it's difficult for any one man to stop any other man, by himself. So we helped out whenever possible.

"I knew Jeff was kind of cold, but I didn't know that Gus didn't score for that long."

After Williams' 19-foot jumper with 9:16 to play in the third quarter, he didn't hit another field goal until 21 seconds remained. And after Malone's 17-foot jumper from the left side with 7:08 to play, he didn't hit another shot from the field, period.

"They didn't make any changes that I really noticed," Williams said. " . . . I took the same shots I did in the first half; all you can do is hope they fall." And Malone said, contrary to the evidence, "I thought I had a rhythm going. And then it was cold. I don't understand it."

Even forward Dan Roundfield added, "I know myself, I missed three or four layups. And when you do that, you start going on a steady roll downhill."

And when the Bullets had scored only 13 points in 18 minutes the second half, it was quite apparent that hill had a steep decline.