Will Hearst, grandson of the late newspaper tycoon William Radnolph Hearst, came to town yesterday to push his new outdoor sports-plus-ecology magazine, Outside. He forgot to shave. "Makes me look like a mountain man, huh," Hearst jokes, sliding into his waiting Cadillac limousine.

Hearst, 28, last October resigned his seat on the board of directors of the Hearst Corp., the massive publishing empire founded by his grandfather, to take the managing editor's job at Outside. The magazine is being published by Jann Wenner of Rolling Stone, who is considered by some to be a modern-day version of the orginal Hearst. The diminution in personal power is substantial, but Will Hearst says the smaller staff and closer ties to "regular people" make the switch worthwhile.

"The Hearst Corp. is very big, it's hard to do anything there," Hearst explained. He said he'd rather be in a small office - Outside's San Francisco staff members 15 - than be stuck in a stuffy New York corporate boardroom. "I want to go where I can meet as many regular people as possible," Hearst said earnestly. "The culture's in the streets."

The newspaper heir's populist leanings - he's a left-wing Democrat in a family of rock-ribbed rightist Republicans - caused some strain after the kidnapping of his cousin Patty in February 1974. But, despite family pressure, Will Hearst refused to move from his walk-up apartment in San Francisco's Russian Hill to the security of a high-rise with a doorman.

"I never could get used to moving in tht corridor of isolation," he said, shaking his head. "Watching you movements, knowing how many exits there are in the theater - that's no way to live."

Will Hearst has seen his cousin Patty several times since a federal judge let her out on bail last Nov. 21. She's gained weight, he said, and seems to be getting her strength back. During her odyssey with her Symbionese Liberation Army captors and in jail later on, she was extremely thin, pallid and sickly.

But the psychological scars from her ordeal under the glaring light of publicity, remain, Hearst said.

"She's depressed and sick to hell of the whole thing," Hearst said. "She told me she can't even try to drive a car because no insurance company will touch her with a 10-foot pole."

He added that his cousin has grown increasingly suspicious of all strangers, particularly those working in the news media. "It will stick with her all her life," Hearst predicted. "Her orientation is to see people as using her to sell newspapers, or leftwing ideology or the ruling class. She's become the Farrah Fawcett Majors of cause."

Despite her anger at the press, Patty is considering a career in "magazine writing," Will Hearst said. He shares her opinion that the media "treated Patty like a piece of meat," but, coming from a newspaper background, acknowledged that the attention "come with the territory."

Will Hearst Hopes Outside, whose first issue comes out later this month with a press run of 305,000, will establish his credentials as an independent force in publishing. He also sees it as breaking down the ultra-conservative image of the Hearst family. "If you let yourself be lumped," he asserted, "you're a lump."

But, despite his determind independence, the family history still lurks in the back of his mind. He's seen "Citizen Kane," the famous Orson Welles movie based on the life of his grandfather, four times and each time the story - which traces a publisher's life from idealistic beginning to his sad, despairing end - frightens him.

"It has a profound effect on me," Hearst said as he got ready for a television appearance. "It makes me wonder and feel sorry for my grandfather. Maybe, I think, it would be better to stay away from this business and settle down on a Western family farm."