OAK PARK, Ill. (AP) _ Vegetarianism may not be in the mainstream of American cuisine, but it's finally escaped the backwaters a few devotees shared with cranks and food faddists.

As recently as the mid-1970s, a young freelance writer wasn't able to peddle an article about vegetarianism even to Chicago's alternative newspapers, which aimed its stories at the young, hip and radical.

''There's no interest in this,'' Paul Obis Jr. said he was told.

The rejection resulted in what is now the nation's most successful magazine devoted to substituting beans, tofu and sprouts for beef, pork and chicken.

Obis - at the time a 23-year-old nurse, freelance writer and vegetarian of three-years standing - took the rejection as a challenge.

He assembled a four-page newsletter in 1974 and called it ''Vegetarian Times.'' He also rejected his own article about vegetarianism for the newsletter, and instead stuffed it with meatless recipes and a subscription card.

''I distributed it to 300 health food stores in the area and got back three subscriptions cards,'' Obis recalled recently. ''That gave us an income of $9 after spending $17 to get the newsletter printed.''

Today, ''Vegetarian Times'' is a four-color, slick publication of 100 pages or more with a circulation approaching 200,000.

The magazine is riding the crest of the nation's health and fitness craze and attracts vegetarians as well as readers interested in cutting down on their use of meat. Obis sold the magazine a year ago ''for a good sum of money'' to Minneapolis-based Cowles Media Co., but stayed on as publisher and editor in Chicago.

There are an estimated 9 million people in the nation who identify themselves as vegetarians, said Lige Weill, president of Vegetarian Awareness Network, a not-for-profit group dedicated to spreading the word.

There are even more who eat meat only occasionally or have cut out red meat, Weill said.

Obis, who estimates that half his readers are non-vegetarians, does not promote any particular type of vegetarianism in the magazine.

Obis and a half dozen editors work at the magazine's suburban Chicago office and handle the stories and recipes supplied by a regular stable of freelance writers.

The magazine includes articles on fitness, health, food and human interest. Frequently the cover features a well-known person, including in recent months children's television host Fred Rogers, baseball manager Tony LaRussa, and Paul and Linda McCartney, vegetarians all.

The recipes, Obis said, are developed by longtime contributors, many of whom authored cookbooks.

Cynthia Cowan, who runs a non-credit vegetarian studies program at Miami Dade Community College in Florida, said she frequently draws on articles and recipes from the magazine for her classes.

Over the past few decades the foods promoted for a vegetarian diet have changed as new health studies appear on the scene.

At one time, vegetarian recipes featured nut casseroles and meals high in cheese and eggs.

''The trend now is away from dairy products and foods that are high in fat,'' said Obis.

The nation's interest in health and fitness has given vegetarianism a respectability and acceptance that wasn't there just a few years back. It's easier for a vegetarian to eat out now, and there's a greater selection of ingredients at grocery stores.

Obis' honeymoon 14 years ago started off with a baked potato for breakfast because that's what the airline he was flying came up with as a vegetarian meal.

''It just amazes me sometimes to think about how commonplace vegetarianism is becoming,'' he said.

End adv for Friday PMs Oct. 18