Clay Felker, the perennial Lazarus of American journalism, is making another comeback--this time as editor of a weekly neighborhood paper serving Manhattan's East Side.

And Philip Merrill, outspoken board chairman of Washingtonian and Baltimore magazines and The Capital of Annapolis, is taking another gamble in the fourth estate--this time by joining Felker in the purchase of the East Side Express, a tabloid with a circulation of around 6,000.

"We've been friends for several years," Merrill said yesterday from Annapolis, "and for the last couple we've been studying various markets. Finally, we both came to the same conclusion about opportunities at the moment." Namely, to purchase the financially floundering weekly and gradually transform it into a major publication. Very gradually, Merrill said: "At first, we're not going to change the format, and it'll be printed on the same press. We're going to practice with it, publish it as an experiment, develop it slowly. I think people will give us time."

He is still smarting from negative community reaction immediately after he purchased Baltimore magazine in 1977 from the city's Chamber of Commerce. "They were expecting to see New York magazine or Washingtonian the very next week!" Merrill said. But eventually he raised the circulation from 6,000 to 40,000. He has a similar goal as publisher of the East Side Express. Beyond that, he would not discuss its future direction.

At present, the paper is not exactly a powerhouse. Since its founding in 1976, it has ranged between 16 and 32 pages per issue, according to former owner Robert Trentlyon, whose company publishes two other community papers serving Chelsea and Upper West Side as well as dance and theater magazines. Trentlyon, who would not disclose the purchase amount, said that by early this summer "we had made a decision to sell it or close it down" because of falling revenues. He was "very pleased" to sell to Felker: "Someone has to come up with a jazzier, flashier product than we did. That's Clay's kind of territory--he knows it much better than we do."

The moribund weekly had concentrated on neighborhood planning news, Trentlyon said. "If you live in an area as large as New York City, you have to belong to something smaller." However, that concept proved "rather difficult" since the distribution area ran from 14th Street up to 96th. Merrill, undaunted, plans an initial circulation of 20,000 "plus a few thousand on the newsstands."

Felker, who has been working as a consultant to Adweek magazine, was vacationing in California and unavailable for comment yesterday. Merrill said Felker has already hired a skeleton staff that includes Jack Nessel, formerly of the The Village Voice and Psychology Today, as managing editor, and "we have enough people to publish immediately." But the details of the sale still have to clear a local court, and Merrill does not expect the first issue until after Labor Day.

Felker, 54, an editorial veteran of several newspapers, Esquire magazine and The Viking Press, founded New York magazine in 1967 and subsequently headed The Village Voice and New West magazine. In 1977, he lost control of New York and New West to Australian press baron Rupert Murdoch. (Murdoch later sold New West to Mediatex, publishers of Texas Monthly, who renamed it California. It was sold again over the weekend to Alan Bennett, publisher of Savvy and American Photographer.) Felker had stipulated to Murdoch that he would not compete with New York magazine. Last year, the agreement expired; and Felker's sudden re-emergence as an editor has prompted some observers to regard the move as an attempt at revenge by waging news-rack warfare with his old creation.

"But we're not competing with New York magazine or The New Yorker, any more than we're competing with The New York Times," Merrill said. "We're publishing a community weekly. We're not in the 400,000-circulation magazine business. There's nothing wrong with that--but there's somebody doing it already."