The College Park City Council voted unanimously last night to approve a resolution recommending extension of a subway tunnel under the city for a portion of the future Metrorail Green Line.

The vote on the controversial issue was taken at the request of Prince George's County Council member James Herl, who proposed the additional tunneling as a compromise between College Park and officials in nearby Riverdale, who had opposed College Park's recommendation in April to move the site of its planned station closer to Riverdale's northern border.

College Park approved Herl's proposal last night despite objections from County Executive Parris Glendening, who declared earlier this week that the estimated $15 million cost of tunneling an additional 600 feet between Rhode Island Avenue and the Calvert Street Metro station at the Baltimore & Ohio Railroad tracks would be unacceptable.

Glendening also said that the current Metrorail plan, which has that portion of the line running on elevated tracks instead of through a tunnel, is in an advanced design stage and that seeking changes would threaten "the future of the entire line."

"I think the signal tonight was clear," an elated Herl said after last night's vote. "It is time to move forward on the route in Prince George's County. All we need to do now is get the county executive to join us. Now only he can hold up the route."

The city's recommendation must now be approved by the Prince George's County Council, the Metro Board, the Maryland Department of Transportation and the U.S. Urban Mass Transit Administration. Metrorail service is not scheduled to be extended to College Park before the 1990s.

In other action, the council adopted a redistricting plan that divides University of Maryland students among three of the city's eight council election districts.

Michael Canning, president of the university's Student Government Association, said the new districts will give students "a good opportunity to control two of the council's eight seats. He confirmed he will run for the council in the November elections.