Billy Cunningham and Pat Riley don't look alike, dress alike, think alike or do much of anything alike.

When they were players they didn't play alike, either.

But when it comes to coaching, even though both have distinctive quirks, similarities abound as both prepare for Sunday's third game of the best-of-seven National Basketball Association championship (3:30 p.m., WDVM-TV-9) in the Forum. Philadelphia leads Los Angeles, two games to none. Game 4 will be at the Forum Tuesday night.

Only four times in the history of the playoffs has a team come back from an 0-2 deficit to win a best-of-seven series.

Cunningham, 39, and Riley, 36, are among the youngest head coaches in the NBA. Both have been extremely successful from the day they took control of their teams.

True, they took over probably the two best teams in all of basketball when Cunningham replaced Gene Shue as coach of the Philadelphia 76ers six games into the 1977-78 season, and Riley relieved Paul Westhead of his Laker duties, 11 games into last season. But there have been trying times for both.

Both Cunningham and Riley are fortunate to have dominant centers and multi-talented players surrounding them. Their basic coaching philosophy is also the same. They believe in giving their players as much creative freedom as they can handle.

The rule of coaching in the NBA is that you're only as good as your players. Cunningham and Riley are believers.

Cunningham, 6-foot-6, was a better player than Riley. He was a member of the 76ers' championship team of 1966-67 and was a four-time all-star. He played in 654 NBA games and averaged 20.8 points in his career, and was also the most valuable player in the American Basketball Association in 1973.

Riley, a 6-4 swing man, was a nine-year playing veteran who averaged 11 points in his best season. He was a get-the-job-done-anyway-he-could player, noted for doing the dirty work and the little things.

As a coach, Cunningham is fiery and animated from the opening tap. He said he has mellowed somewhat over the years.

"I don't think it takes as long for me to get over a loss as it used to," he said. "I don't think I leave as much of myself out there on the floor now."

Riley was always mellow.

"I'm still learning and having fun," he said. "Things happened so fast I haven't had much time to do much reflecting. But I know I must be one of the luckiest guys in the world. I always wanted to be a coach, but I never dreamed it would be with one of the greatest teams ever."

Riley's approach is to let the players play. "It's their game," he said. "You've got to let them play. My job is to organize and prepare and give them direction when they need it."

Lakers owner Jerry Buss, in hiring Riley, said he wanted someone close to the team who he knew would get along with the players. He wanted things to continue smoothly.

The 76ers wanted a major shakeup when they chose Cunningham.

"The team was a collection of all-stars, but even with all its talent, it had become blase and nonchalant, " said General Manager Pat Williams. "Billy was precisely what we needed--someone to relight the fires. His enthusiasm was contagious."

Cunningham has gone on to win 200 games and 300 games faster than any other NBA coach.

Cunningham seems less outgoing than Riley. His postgame interviews last about five minutes; there are few questions and he retreats to the dressing room. Riley talks for 20 minutes and goes into as much detail as needed to get his points across.

Riley doesn't have much experience, but he will have to come up with something to turn this series.

"We're still optimistic," he said. "We're the champions, remember."