A plan by a Prince George's County Council member to tunnel a portion of Metrorail's future Green Line through College Park has drawn opposition from County Executive Parris Glendening, who says it jeopardizes the entire line.

The county executive, commenting on Council member James Herl's proposal last week to tunnel much of the Green Line's route through College Park rather than run it on elevated rails, said that design is already in an advanced stage and seeking changes would threaten "the future of the entire line."

"This is a risk we must not take," he concluded. Glendening also said the $15 million the tunneling would add to construction costs would have to be paid by county taxpayers, who cannot afford it.

Metrorail service is not scheduled to be extended to College Park before the 1990s.

Herl yesterday called Glendening's opposition "totally off base," adding: "The county executive doesn't set policy, the County Council does." He and College Park officials maintain that the added cost should be borne by all of Metro's jurisdictions since the tunneling would solve an environmental problem.

The College Park City Council is expected to approve Herl's proposal tonight. Eventually it will be taken up by the County Council, the Metro board, the Maryland Department of Transportation and the U. S. Urban Mass Transit Administration.

Existing plans for the route call for an elevated track beginning near the intersection of Albion Road and Rhode Island Avenue at the southern edge of College Park. The City Council recommended approval of that alignment in 1979, but changed its position in April in response to complaints that the elevated track would come within 90 feet of many homes. The council also voted to move College Park's proposed Calvert Road Metro Station to a site just north of Riverdale.

Herl, who represents both cities, refused to take the issue back to the County Council until a compromise was reached because Riverdale officials objected to the change. Under Herl's proposal, the original alignment approved in 1979 would remain, but instead of an elevated track the line would continue underground an additional 600 feet past the homes nearest the line.

Because the College Park station originally proposed would necessitate closing Calvert Road--which connects Rte. 1 and Kenilworth Avenue--to through traffic, Metro officials have proposed building a new highway--the Paint Branch Parkway. Herl's plan would place that highway in Riverdale and south of College Park.

Those who favor Herl's plan call Glendening's position inconsistent. College Park City Council member Chester Joy, who has led much of the opposition to the Calvert Road station, said that building the parkway in College Park would cost considerably more than building it south of the city.

"I'm not trying to delay anything, I'm trying to get this thing constructed," Herl said, saying that a group of College Park citizens could easily delay the Green Line in court as opponents of a Green Line southern alignment have done.

Glendening said yesterday he is willing to work with College Park officials on Metro's impact, "but not to the extent of $15 million."