When "The Love Boat" was launched seven TV seasons ago, there were a lot of people out there ready to torpedo it. People like Carol Burnett. And Kojak. And TV critics.

"They likened the show to the Titanic," said the Pacific Princess' skipper, Gavin MacLeod, recalling how television critics didn't like the show -- and generally still don't. They predicted -- or hoped -- it would sink to the bottom of the Nielsen ratings. "We came on Saturday night opposite 'The Carol Burnett Show' and then 'Kojak,'" he recalled, and outlasted them both to become a dominant show on Saturday night.

As Capt. Merrill Stubing, MacLeod has been at the helm of "The Love Boat" since it set sail, heading a cast- crew ensemble that has weathered storms of criticism and navigated its way into viewers' hearts. Fittingly, the captain never doubted it would happen.

"My agent presented 'The Love Boat' with reservations," MacLeod recalled. "I thought they had every base covered -- characters everyone could like, poignancy, guest stars and three stories each week. I said, 'If this doesn't go, I don't know commercial television.'

Gavin MacLeod knows commercial television. In a business in which the odds do not favor a series' lasting from fall to spring, MacLeod has been part of two that have lasted 15 years and will be in reruns as long as there is television. "I've been very fortunate," he said. "I've picked the right pieces."

The two pieces viewers know best are his roles as Stubing and as Murray Slaughter, the head news writer and resident tart-tongue on "The Mary Tyler Moore Show." Between those two roles, MacLeod has been a fixture on Saturday's prime-time television since the fall of 1970. And inveterate late-movie watchers often find themselves squinting at villains on the screen and asking, "Is that Capt. Stubing?" It probably is.

MacLeod got an early start toward being type-cast as a bad guy when he was a young man working as an usher at Radio City Music Hall, wearing a second-hand toupee (he was bald at 18) and looking for a break as an actor. It came when he landed the part of a junkie in the Broadway production of "A Hatful of Rain" with Shelley Winters and Tony Franciosa. He later went west and played a similar character on stage in Los Angeles with Robert Blake in "The Connection."

But under the skin of the villainous character actor, he said with a smile, "there's a little Irish poet." He recalls breaking the bad-guy mold with work on such TV series as "My Favorite Martian" and "The Big Valley." In all, he has made 35 movies and about 350 TV appearances.

He took a step toward a share of television immortality when he was invited to audition for a part in the universally revered "Mary Tyler Moore" series. He was slated to play Lou Grant.

He recalls that he got "respectable" laughs delivering Grant's lines -- "You've got spunk," he growled at Mary. "I hate spunk" -- but didn't feel comfortable with the part. "I was on a diet, I was rehearsing 'Carousel,' I was thinking thin," he said. "I felt young. I'd known Mary from earlier days, and I felt I was her contemporary, not older." So he asked to read for the part of Slaughter, one of whose jobs was to keep anchor Ted Baxter's over-sized ego at least semi-deflated. "There he is," he said to Baxter, "the Mastroianni of Minneapolis." This time, he recalled, the producers' guffaws were more than just respectable. And as he left them laughing, he passed Ed Asner pacing in the waiting room.

When the "MTM" show finally folded, he recalls seeing four TV scripts. He chose to go to sea. "When a door closes," said MacLeod, "another opens."

"The Love Boat" took the three- love-stories-in-one form of "Love, American Style" and put it on a ship. The multi-storyline format has since become a trademark of Aaron Spelling productions, but the idea of launching the cast on a trip that detaches them from day-to-day reality for romance, fun and quasi self-discovery has gone largely uncopied. "SuperTrain," for one, tried and failed. In addition to making waves in television circles, "The Love Boat" is credited with helping to put new life into the cruise- ship industry.

"The Love Boat" has encountered a bit of rough ratings water this season, but seems far from going under. MacLeod sees the need for the show to change if it's to avoid being moth- balled. "There's an attempt being made to flesh out the regulars," he said, "give them more to do and extend the dimension of the show." Another change, he suggested, might be to put the show aboard a new ship, perhaps one of the super-cruisers the show has helped spawn.

MacLeod's 15 years as a Saturday night TV fixture have corresponded roughly to a period that required him to put his own life on a steadier course. "In 1971," he recalled, "I was very sick." His doctor recommended that he stop smoking and drinking and cut red meat out of his diet. He did. Now, at 53, he appears fit, trim and energetic. And he tells terrific Weight Watchers stories, like the one about the woman who needed a chocolate fix late at night after the stores had closed. In desperation she called Western Union and sent herself a candygram.

A divorced father of two sons and two daughters, aged 20 to 25, MacLeod appreciates that his kids have grown up straight and acknowledges that he didn't realize the problems they had being children of a celebrity. After all, there had always been enough money in the family, and each child had his own car -- though only second hand. "We had a pow-wow and they told me how hard it was to have me for a father," he said. "They became leery of their friends. Kids kept coming around them just because of who their father was. They started not telling whose kids they were when they changed schools."

MacLeod's earning power has enabled him to extend his family, in a sense, and contribute to charities that interest him. He supports four girls in Zaire, the Philippines, India and Bolivia. He's never met them. His other interests include Boys Town in Omaha, Neb., for which he's a national spokesman, and the national cerebral palsy telethon.

He's started a production company -- called MacLeod Nine -- and has on the burner a movie-of-the-week that could, he says, become a series. He also entertains the thought of producing and playing in a Broadway show.

Meanwhile, he spends nearly two months a year at sea on the Pacific Princess while the series films location material, then prays for harsh weather while he's ashore. The worse the winters, he reasons, the more pleasure viewers take in switching on the tube Saturday night and watching "The Love Boat" cruisers escape real life.

"People turn on the television and see pretty girls in bikinis, people making love, the sun," he mused. "Most of the mail I get, people say thanks for making them feel good. We give them happy endings."