Edward Kosner, currently a CBS vice president and former editor of Newsweek, was named editor of New York magazine yesterday.

Kosner, who was ousted from Newsweek last summer, replaces Joe Armstrong, who had been editor-in-chief and president of New York and New West magazines for 2 1/2 years.

New York, the weekly prototype for the slick city magazines, was acquired by Australian press magnate Rupert Murdoch nearly three years ago. Neither Armstrong or Murdoch was available for comment.

Sourdes at the magazine said that increasing staff dissatisfaction with Armstrong, and policy differences between Armstrong and Murdoch, led to the ouster. When asked what Armstrong's future plans were, an assistant said he has none, since "he just heard about it today."

Kosner, who will take editorial control of the magazine Monday, said Murdoch lured him to New York with a "very attractive offer and the opportunity to edit a very important magazine." He said he planned no major changes in the product. "The only thing I would say is we'll do things first and do them best."

New York is an admixture of general features, political reporting, celebrity profiles and arts critism, along with several gossipy columns and service articles. The magazine was founded in the late 1960s by Clay Felker, also publisher of The Village Voice. In the mid-'70s, Felker founded New West.

Murdoch took over the Voice, New York and New West in 1977. The Australian publisher also owns The New York Post, the city's only remaining afternoon newspaper, which has been losing millions of dollars a year.

Murdoch's other U.S. holdings include The Star, a weekly tabloid with national distribution, as well as several San Antonio newspapers.