NEW YORK (AP) _ Hollywood's clout on television is ebbing. The Academy Awards ceremonies last week drew their lowest ratings ever, and even a popular trouper like President Reagan doesn't do as well in the A.C. Nielsen ratings as does Boy George.

They remained popular enough, however, to lift ABC into a first-place tie with NBC last week, according to the ratings released Tuesday. The awards had the third-highest ratings for the week, 27.3 or 43 percent of the viewing audience, while Barbara Walter's interview with President and Nancy Reagan tied CBS' ''60 Minutes'' for 10th place with a rating of 20.9.

Last year, Ms. Walters led into the Oscar show with guests including Boy George, the androgynous British troubadour, and got a 25.2 rating.

NBC, which has clinched first place for the season with three weeks still to go, had the top two programs: ''The Cosby Show'' with a rating of 32.0 and a 54 share, and ''Family Ties,'' with 28.5 rating and a 47 share. ''Cheers'' on NBC was sixth with a 22.3 rating and ''Golden Girls'' was seventh with 21.8.

In addition to the Oscars and Ms. Walter's special, ABC had ''Who's the Boss?'' ranked fifth at 22.5 and the premiere episode of ''Perfect Strangers'' eighth at 21.3.

CBS' ''Murder, She Wrote'' was fourth for the week at 23.7 and ''Mrs. Delafield Wants to Marry,'' a TV movie starring Katharine Hepburn, was ninth at 21.0.

Each rating point represents 859,000 homes; the share reflects the portion of the sets in use during a particular time period.

For the week, NBC and ABC each had a rating of 15.8, while CBS lagged at 14.2 and finished third for the first time since November. After 27 weeks of the prime-time season, NBC leads with an average rating of 17.7, followed by CBS with 16.7 and ABC with 15.0.

Though the Oscars got a big audience, chosen by 43 percent of all the sets in use that Monday night, it wasn't the huge audience of years ago. In 1960, the awards pulled an 81 share, and as recently as 1983, the show had a rating of 38.0 and a 59 share.

''The movie audience isn't necessarily a television audience, and that's reflected in the lower level of viewing,'' George Keramidas, ABC's vice president for research.

Gerald Jaffe, his counterpart at NBC, observed that in recent years, films have also lost drawing power on television.

CBS still had no luck finding an audience for ''Mary,'' the new Mary Tyler Moore show, and ''Foley Square.'' ''Mary'' had a 9.8 rating and ''Foley Square'' had a 9.0, putting both near the bottom of the rankings in their first outing in the 9-10 p.m. time slot Tuesday. Both had struggled in the 8 p.m. hour on Wednesday night as well.

ABC got encouraging ratings for two new shows on Friday: ''Mr. Sunshine'' finished 44th for the week with a 13.2 rating and 23 share, and ''Joe Bash'' was 49th with an 11.3 rating and 19 share. Both, however, had the luxury of opening on a night when ''Dallas'' had been pre-empted on CBS.

''Perfect Strangers,'' which was helped by following the hit ''Who's the Boss?'' on Tuesday night, got one-third of the audience in its time slot. Its competition on CBS, the debut of ''Morningstar/Eveningstar,'' attracted only 15 percent of the audience and a rating of 9.7