Jann Wenner, the erratic wunderkind editor of Rolling Stone, will replace Bob Gutwillig as editor of Look today.

In a related move, Look will become a monthly publication following the release next Monday of its eighth issue, featuring Barbra Streisand on its cover.

Wenner discussed the move in some detail yesterday afternoon, although Gutwillig would neither confirm nor deny the changes. They have scheduled a joint press conference in New York this morning.

Wenner became one of the enfants terribles of the publishing world in 1967 at the age of 21, when he founded Rolling Stone. At first that publicatin was an intergral part of the social upheavel of the '60s, but later became established as the Wall Street Journal of the counterculture's increasingly more conventional life style. The focus of the magazine broadly followed Wenner's own interests, beginning with music and serially evolving into a forum for new journalism, political reporting and - most recently with the magazine's move from San Francisco to New York - tales of high society's glitter and glamor.

"I'll remain editor and publisher of Rolling Stone," Wenner said yesterday. "Rolling Sone will stay the same. I haven't been that involved with the day-to-day operation lately. It's very effectively manageed right now. I won't take any of the editorial staff to Look, but we'll combine the financial and circulation departments.

The surprise changes, completed over the weekend, marked the second time in one week that a major national magazine has been taken over by a young editor, with frequency of publication changing from biweekly to monthly. Last week Esquire was bought by two young University of Tennessee graduates, who named themselves editor and publisher and announced plans to revert it to its monthly format this summer.

Wenner yesterday denied reports that he was negotiating an agreement to sell Rolling Stone to Australian publishing mogul Rupert Murdoch.

"I've talked to a lot of people who are interested in the magazine, but Murdoch isn't buying it," Wenner said. "And now with two magazines, both of them will be much more cost-effective."

Wenner also denied reports that Rolling Stone was in financial trouble.

"On June 30 we'll complete our most profitable year ever," he said. "We've got 645,000 subscribers now and we'll be guaranteeing 650,000 to our advertisers at the end of the summer."

Look recently raised its circulation guarantee from 600,000 to 700,000. Although the magazine has been praised for its vital, newsy appearance, it has been beset with personnel problems. Fifteen members of the editorial staff have been fired since January 1, including managing editor John Durniak. In an unrelated move, executive editor Marianne Partridge quit. Sources at Look expect other staff members to depart after Wenner arrives.

"The current editorial staff will have to be reduced, given the reduced frequency of publication," Wenner said. "I want to aim the magazine at a younger audience, cut out the gossip columns, make the articles more timeless and give it a more elegant design.It'll be less photo news, but still a photo magazine, using the best photographers, like Scavullo, Avedon, Hiro, Annie Leibovitz - people we use now at Rolling Stone."

Wenner will not be acquiring the magazine, "although I'll be sort of an owner," he said. He would not disclose the financial arrangements of the deal. Daniel Filipacchi, owner of Paris Match, will remain publisher of Look.

Sources close to Gutwillig said yesterday that the switch of publication frequency at Look was coming because "the magazine is selling a lot of copies and losing a lot of money." The sources describe Gutwillig as "ambivalent and relieved" about his replacement. CAPTION: Picture, Jann Wenner