Plans were unveiled yesterday for a 12-story office tower to be built atop the present Metro bus terminal and the planned Metro subway station at the northeast corner of Wisconsin and Western Avenues in Friendship Heights.

The project would create a covered "kiss and ride" station serving both bus and subway riders.

It would be the most extensive project ever jointly developed by Metro and a private developer, the board of the Washington Metropolitan Area Transit Authority was told yesterday.

The developer of the proposal would be The Chevy Chase Land Company, owner of the Chevy Chase Shopping Center and of the pie-shaped property at Wisconsin and Western where a Howard Johnson restaurant once stood.

The old Howard Johnson site and the present Metro bus terminal land would be combined and the transit terminal-office building complex built on the whole property.

The joint development would save Metro the $1.8 million cost of buying the Howard Johnson site for a subway station, the Metro board was told. The developers would also pay for the new bus terminal.

The developers in turn would get air rights to build a larger building.

The area already is zoned for a high-rise office building, but the project would require approval of Montgomery County building officials and the county council. Public hearings are required on the project, which could be apposed by community groups that have in the past objected to major developments in Friendship Heights.

Metro officials estimated the office building would cost about $14.4 million to build, not counting the cost of land and the subway station.

The plan is to work on the office tower and the subway station simultaneously, to minimize the cost and simplify the construction work.

Metro tunneling is already under way more than 100 feet below the Wisconsin-Western Avenue intersection. The timetable calls for starting the office building in January 1981 and completing it in the summer of 1982. The subway station is scheduled to open early in 1983.

The Bethesda firm of Bagley-Soul-Lee Architects has been hired to design the building, said Hunter Davidson, president of Chevy Chase Land. The firm is one of Washington's oldest developers; it developed most of the property along Connecticut Avenue north of Van Ness Street.

Discussions between the developers and Metro officials have gone on for several years and the final proposal went to the Metro board yesterday. No formal action was taken, but Metro officials said the board has endorsed the concept.

Plans and sketches unveiled yesterday show four levels of parking beneath the building site and a 240,000-square-foot office tower set back from the Wisconsin-Western intersection.

The entire site would be covered by a deck one floor off the ground; a four-story glass enclosed court would be built atop the deck at the point of the pie-shaped property.

A second-floor foot bridge across Wisconsin Circle would link the building to the Chevy Chase Shopping Center.

The subway entry, the bus terminal and the office building lobby would be at ground level. A subway entry is also being built into the lower level of Mazza Gallerie, just across Western Avenue in the District of Columbia.

Another subway entry is planned at the south end of the Friendship Heights station, surfacing where the Metro bus garage is at Wisconsin Avenue south of Jenifer Street.

Metro real estate director Henry Cord said the transit agency has done joint developments with private builders at Rosslyn and at 1101 Connecticut Ave. NW, in downtown Washington.

But the office, bus and subway complex is the biggest so far for Metro, which is seeking a developer for a similar complex at the Van Ness subway sattion on Connecticut Avenue.