Mike Warren, the slim, handsome captain of the UCLA basketball champions of 1967 and 1968, remembers the day he auditioned for a small part in the movie "Butterflies Are Free." He expected no trouble because the producer, Mike Frankovich, also had been a star athlete at UCLA.

Instead, he had to fight for the part, coming back four or five times for readings before Frankovich was satisfied. "It brought me crashing down to reality," Warren said. "It taught me early in my career that anything I got I was going to have to get on the merit of my acting ability."

Today, as one of the stars of NBC's "Hill Street Blues," Warren is better known than he ever was as an athlete. Yet he is so intent on burying his athletic past that he insists on the billing "Michael Warren," one more way to erase memories of the 5-foot-11 guard whom former UCLA Coach John Wooden still calls "one of the smartest basketball players that I have ever seen."

Ed Marinaro, the muscular Cornell back who once set an NCAA career rushing record, veteran of two Super Bowls with the Minnesota Vikings, has joined Warren on the "Hill Street Blues" cast.

Marinaro recalls with perverse delight the jokes that greeted his first audition for the show ("Hey, Ed, we have a game at the park every week," Michael Kozoll, who helped create the series, had said), followed by astonished looks as he carried off a sensitive love scene. The assembled producers had him repeat it, to make sure it wasn't a fluke.

"Hollywood exploits the athlete," Marinaro said with a smile and a shrug. College and professional stars arrive here each year to enroll in acting classes, hire agents and wait for the offers to flood in. Most never make it. Some, like Johnny Weismuller and O.J. Simpson, succeed largely on their names and looks alone. But some, like Paul Robeson, Chuck Connors and John Wayne, have eventually, through dramatic talent and effort, forced audiences to think of them primarily as actors.

With parts on network television's most celebrated and unconventional dramatic series, Warren, 36, and Marinaro, 32, seem well on their way to obliterating their athletic glory days. For that, both say, they can thank the short-sightedness of pro coaches and owners who cut their athletic careers far shorter than either of them would have liked.

Warren, recruited from the South Bend, Ind., high school where Wooden once coached, was floor leader for the first two of Kareem Abdul-Jabbar's three championship years at UCLA.

Warren possessed a court sense and ability to make quick decisions that Wooden still raves about. But Abdul-Jabbar (then Lew Alcindor) dominated college basketball, and Warren thinks that experience helped him adjust to his life in a television ensemble company.

"On Hill Street, Dan (Daniel J. Travanti, who plays precinct captain Frank Furillo) is the focal point," Warren said. "If there is any star, he is probably the person who gets the most attention, and perhaps if I had not had the kind of experience I had at UCLA in working on a team with Kareem, this kind of experience might have been a little more difficult."

Upon graduation, Warren had a degree in motion picture production and direction, his long-range career goal, but he still hoped to try pro basketball. He wanted $50,000, laughably low in today's market for the captain of an NCAA champion, but his size did not endear him to the pro scouts. The Seattle SuperSonics offered $10,000 and the Los Angeles Stars of the American Basketball Association, where he wanted to play, offered only $15,000.

With little regret, Warren chose Hollywood, where he scratched for small jobs as a producer's assistant or consultant and made ends meet by turning his love of photography into a sideline business preparing photo portfolios for struggling young actors.

He first became acquainted with his wife Susie, now a Montessori school teacher, when he offered to take some portfolio pictures for her. They married, had a daughter, Kekoa, and then a son, Cash. According to his sister, Jenelle Brown, Warren "never got caught up in that Hollywood stuff."

Warren kept a few close friends from college, such as freshman dorm-mate Anthony Alexander, now an attorney, and basketball teammate Kenny Washington, now a banker. "We got too old for basketball," said Washington, 38, so they played a lot of tennis.

Yet memories of Warren's basketball days in this UCLA-crazed town helped open the way for opportunities to try out the rudiments of producing and do some acting.

"I had an image of the actor, and it was such a negative image. It was a person who was egocentric, and so self-centered that other people did not matter," he said. "I thought I would lose part of me if I became an actor."

Film director Bert Schneider hired him as a technical adviser on the movie "Drive, He Said," which dealt with college basketball. Warren also got a part in the film. He did commercials and small television roles, while continuing to study acting with private coaches.

Finally, he won a guest appearance as a high school basketball player on the television series "The White Shadow." He was encouraged by his wife and his agent to take it, even though he disliked basketball parts and felt he could not play a 17-year-old.

Warren developed a friendship with the show's director, Jackie Cooper, who steered Warren to a role in the short-lived series "Paris," starring James Earl Jones. "Paris" was written and produced by Steven Bochco, the man who was to soon join Kozoll in creating "Hill Street Blues" and cast Warren as Officer Bobby Hill.

"Bobby Hill is sensitive and compassionate to a fault," Warren said. "I think he is a much better person than I am. I think I'm a nice human being, but some things he tolerates I would never tolerate. I mean, I would never tolerate a person like Andy Renko (Hill's defiantly redneck partner played by Charles Haid), not day in and day out."

Like Hill, Warren says he is leery of joining political organizations and remains disillusioned by the failure of other black athletes to boycott the 1968 Olympics as he and Abdul-Jabbar did.

He also bemoans the lack of opportunities for black actors. He recently won the NAACP's Image Award for best performance by a black actor in a television drama. But he also noted the awards committee found only one black actress, Cicely Tyson, in a major movie role last year that would qualify for the film actress award. "That's pretty sorry," Warren said.

Only 4 1/2 years past the day he quit pro football for good, Ed Marinaro has less acting experience and training than Warren. But he has been studying for six years, ever since an acting workshop he took on a lark in 1976 and found to his astonishment that it changed his life.

Marinaro had come to Los Angeles to spend some time with his friend Joe Namath during the off-season in which he jumped from the Vikings to the New York Jets. The college career of Marinaro, a 6-2 1/2, 220-pound running back, remains one of the great what-if's of all time.

He broke nearly every rushing record of his day, gaining 4,715 yards over three years for a 174.6 yard per game average. Yes, he played for Cornell, and football scholars still argue whether his totals would have been higher behind a full-sized Big Ten line, or lower if subjected to defenses more formidable than those found in the Ivy League. The doubts may have cost him the Heisman Trophy, which he lost in 1971 to Auburn quarterback Pat Sullivan.

Marinaro said he rejected 40 or 50 football and basketball scholarship offers, deciding instead to let his father, who owns a sign painting company, finance his way through Cornell's hotel and restaurant management school. To this day he thinks it was the right decision.

"In your life it gives you a feeling of superiority," Marinaro said while sitting in the NBC commissary. "Maybe it is wrong to feel that way, but I'm so proud of the fact that I went to an Ivy League school and graduated from an Ivy League school."

He graduated from high school in New Milford, N.J., a town full of people with Italian names. In college, he enthusiastically immersed himself in what he calls the "macho sports" culture available to athletes, and he stayed away from the political activities that were shaking up consciousnesses on the rest of the Cornell campus.

Pro football was no less limited, so when he first stepped into the Los Angeles acting class he got a shock: "People are up on the stage crying and really exposing themselves and making you really uncomfortable and you're saying, 'Hey man, what am I doing this for?' "

Bit by bit, he began to appreciate what he was being taught, particularly the need for vulnerability--"to show how you're feeling." It was somewhat disconcerting to take these awakening feelings back to the New York Jets: "On the scouting reports they don't say: 'We like this kid. He's a real blue chipper. He runs a 4.6, very vulnerable.' "

Yet, by the seventh game of the 1976 season, Marinaro said, "I was playing my best football . . . I was finally getting some personal satisfaction out of the sport. I had two 100-yard rushing games in a row, something I had never done in Minnesota in four years."

But in that seventh game in Foxboro, Mass., George Webster of the Patriots landed on Marinaro's foot, bending it back in a way that would take almost a year to heal. Marinaro eventually was cut from the team, and he says he lost his enthusiasm for the sport. He served briefly with the Seattle Seahawks and tried out for the Chicago Bears, but no one seemed interested in playing him and he decided to return to Los Angeles for good.

He won a small part in one episode of the series "Eischied," joined a trio of male "Charlie's Angels" on a pilot that did not succeed, then mesmerized the producers of the comedy series "Laverne and Shirley" with his performance as Laverne's cousin from Italy.

In his acting class, Marinaro had been working on the part of an Italian in the play "The Rose Tattoo," so when the Laverne and Shirley reading came up, his accent was perfect. The show's producers found a full-time role for him as "Sonny St. Jacques," the muscular stunt man who worked as caretaker of the girls' California apartment building.

Marinaro's athletic skills remained important, for he often made his entrance hanging upside down in the girls' apartment window. He was a handsome, single actor beginning to make good money, getting admiring fan mail from women and seemingly at the start of a real success.

Then "after 13 shows . . . they called me and said they weren't picking up my option for the rest of the shows," Marinaro recalled. "The character just wasn't working, you know . . . It was like getting cut from the football team. That was sort of a devastating blow, you just think you're never going to work again. It affected me for a couple of weeks until I said, hey, you know. . . all right . . . REGROUP!"

A month later, he won the role of Officer Joe Coffey on "Hill Street Blues," a temporary character scheduled to appear in four episodes before being killed by a shotgun-wielding motorist. "I said, what the hell, I'd get four hours of dramatic film," Marinaro said. "People in this town when you go up for an audition they say, 'Have you any film on you?' I'd say, 'I got Laverne and Shirley,' and they'd say, 'Ah, no, do you have anything else?' "

But Marinaro loved and nurtured the role, developing an intriguing relationship with the hard-nosed policewoman played by Betty Thomas. The producers noticed and wondered if they should really kill off Officer Coffey. While filming the last scene, before Marinaro heard the good news that he would recover from his wounds, the director told him, "Ed, Joe Coffey's life is in the hands of your agent." Sure enough, a new contract was negotiated for him to return this season.

Warren and Marinaro have become friends, occasionally discussing on the set the joys and frustrations of athletics and acting. Their athletic activities are confined to less strenuous sports like tennis, although both performed in a recent episode as stars of the precinct basketball team challenged by a team of young hoodlums.

Marinaro calls Warren "a wonderful actor," and shares Warren's complaint about onlookers who fail to appreciate the years of work and study it has taken to learn to project emotion on film. "One thing that people say to me that really gets me," said Marinaro. "They say, 'I see a lot of you guys are getting into acting now.' "

Asked about Marinaro, Warren delivers the sort of insult expected of a Hill Street regular. "Marinaro's a jock," said Warren, then flashed a huge grin.