NEW YORK (AP) _ A Japanese college plans to open a private high school here - the first of its kind in this country - to prepare children of Japanese businessmen and women for the rigorous college admission standards in Japan.

''Japanese parents living here will be very, very happy about this,'' said Junichi Kogo, a representative of Keio University, which plans to build the school on the campus of Manhattanville College in Purchase.

''It is going to fill and important gap in the education of children whose parents are pleased to be working here, but are concerned that their children will lose the flavor of their Japanese heritage and not get into fine Japanese colleges.''

Plans for the school were jointly approved Saturday by administrators from Keio University and the Manhattanville board of trustees, The New York Times reported today.

Both schools now must apply for zoning permission from planning officials. If approved, the school could be in operation by the fall of 1990, the newspaper said.

The Japanese Ministry of Education operates a private elementary school in the borough of Queens, but there is no high school for Japanese who want to maintain their language skills while in the Unites States.

The planned, coeducational school would offer students from grades 10 through 12 a blend of traditional American and Japanese curricula with emphasis on college preparation.

About 400 students are expected for the first year and 750 within five years, said Martha Savage, president of Manhattanville.

About 60,000 Japanese live in the metropolitan area, according to city estimates, but many are here temporarily. About 11,000 Japanese nationals live in suburban Westchester County, where the school is located.

''This preparatory school is a sign of the times,'' said Laura Kaufman, chairman of the Asian studies department at Manhattanville. ''The Japanese business community has settled here for the long haul.''