Some here are calling it "Mcnamara's Revenge," the final act in a tragicomedy that has played this island for almost a decade.

The leading man was World Bank President Robert Mcnamara, usually type-cast as the villain because he and three partners had bought property in 1972 that included a strip of beach which was a favorite of skinny-dippers.

When Mcnamara tried to restrict bathers' access to it, he was never quite forgiven. Under his stewardship, the beach became a cause, symbolic to some here of what was wrong with America in general and the establishment in particular. Some saw it as the easternmost front of the Vietnam War even though Mcnamara had not been secretary of defense for almost four years.

Then actor John Belushi recently entered stage left, buying out Mcnamara for $425,000. Belushi, of "Saturday Night Live" and "Animal House" fame, will take possession Sept. 17 of the four- year-old, four-bedroom contemporary house on 8.5 choice south coast acres. In addition, he will assume a quarter interest in a tennis court and common land which includes part of Chilmark Pond.

McNamara could not be reached for comment. His office did confirm he intends to participate in a California agricultural business venture with his son. The spokesperson, however, said she did not know if that was the reason McNamara sold his Vineyard property.

Belushi, reached in Chicago where he is on location for a movie, declined to comment on the purchase. The price reportedly is $100,000 under the property's fair-market appraisal. Belushi's offer also was first made to McNamara.

News of the sale raised a few eyebrows and prompted a few chuckles among islanders who have relished their front-row seats at the Chilmark "drama" throught the years.

Some islanders are calling the sale "McNamara's Revenge" because the colorful Belushi, the complete antithesis of McNamara, is an unknown quantity: Will he be a quiet, reclusive movie star (like Mia Farrow or James Cagney) or a noisy party boy?

"Nobody knows if Belushi is wild or straight," said one amused Edgartown resident.

Singer Carly Simon (of the Simon & Schuster Simons) and her husband, singer James Taylor, who live here year-round and own the island's only disco, have often hosted Belushi and his wife, Judith Jacklin, during their visits here.

"He doesn't know what he's getting into," Simon said the other day, "or that he's going to inherit all the Mcnamara karma as well."

Simon said it was her brother, photographer Peter Simon, who first brought the Mcnamara property to Belushi's attention.

"I really doubt John even knew who Mcnamara was, other than having some vague awareness that he was once a Cabinet officer," she said.

Peter Simon more circumspect about the Belushi purchase or his own role in it, said Mcnamara "could not have sold it to a nicer guy."

Peter Simon was often in the foreground of local activities protesting the Mcnamara presence. A relentless crusader for open beaches throughout the Vineyard, Simon took after Jacqueline Onassis a year ago to open up beaches in the 375-acre ocean-front tract she bought for $1.5 million.

"There are a few here (like Peter Simon) who think everybody's beaches but theirs should be public," said an Edgartown businessman who has followed the controversy over the years. "I wouldn't put up with it."

In contrast, "private beaches in Massachusetts seem to be owned by certain people," said a New York attorney involved in the original sale to the Mcnamara group. "If you're one of the certain people, it's okay. If not, too bad."

By buying out Mcnamara, Belushi automatically buys into the original partnership that included Washington attorney David Ginsburg, ITT executive Richard Hodgson and the late New York financial consultant Ralph Meyer.

Today, the group's land includes four lots of more than eight acres each, although originally the tract was comprised of 41.46 acres. In accordance with their own purchase agreement at the time, the partners turned over a 4,000-foot stretch of beach, now known as Lucy Vincent Beach, to the Chilmark Town Association. Only Chilmark residents who pay a set fee may use the beach.

Ginsburg's parcel-with 425 feet of prime ocean frontage-also has gone on the market, bearing a price tag of $225,000. One islander says the action was "prompted" by Belushi's purchase of the Mcnamara land.

Ginsburg, who has a contract on the property, however, said yesterday his decision to sell had nothing to do with Belushi. "I was planning to do it long before that."

Unlike Mcnamara or Meyer, Ginsburg said he never built a house there because "It's a very expensive thing to build on the Vineyard. After I bought that property, I bought some property in Alexandria. All the where-withall I have is going into that."

Belushi's celebrity could create a new set of problems for bathers who frequent the partnership's 1,900 feet of private shoreline, despite posted signs advising it is closed to the public.

"He's a public figure who might lost his privacy because a lot of young kids would want to climb up and see where he lives," said a Belushi friend. "He'll be subject to the whim of three other people, so he can't do anything on his own without their approval."

Still, "much better Belushi than Mcnamara," said a Boston University co-ed the other day, the morning's first trespasser on what is called "Mcnamara's Beach." "My feelings about it are largely political. My politics are at the other end of the spectrum from his."

Mcnamara's "politics" combined with his efforts to keep his beach private-and clothed-so enraged one young islander that he tried to push Mcnamara overboard on the ferry at Woods Hole in 1972. Mcnamara never brought charges.

It was not quite the type of "aggression" islanders had in mind when they used to talk about Mcnamara's defensiveness over "social aggression." He was a man, they would say, "who would come in with the fog and go out with the tide."

Posting his beach, once part of the nude "Jungle Beach," seemed "very governmental, very Pentagon-like," recalls a Chilmark resident. "That's when the atmosphere changed."

For his part, Mcnamara voiced concern over the fragility of his property.

"How do you ensure that the public use doesn't destroy the loveliness of the area?" he once asked.

Erosion claims an average of five feet of land annually along that stretch of beach, according to a study by the U.S. Army Corps of Engineers.

Mcnamara's low-lying house,situated some 300 paces back from the bluff, is built with laminated beams and sits on concrete piers so that eventually it could be moved if erosion becomes critical.

Some here feel Mcnamara was the hapless victim of an unwarranted bum's rush and that, actually, Chilmark "lucked out" when the Association received the three-quarter-mile stretch of beach, estimated to be worth $150,000.

"But you know how it is," said one Chilmark resident, "nobody loves a giver. The whole business was a continuous headache for him. It was a stronghold at times of anti-vietnam people and he was a visible sign."

Reports persist that Mcnamara never quite reconciled himself to skinny-dipping at his front door.

One story making the rounds is that the final straw came recently when he and his wife, Margaret, went to their beach and found a film crew making a blue movie. Before they could escape, the rumor goes, the Mcnamara were photographed in the background.

Others who frequent the beach say in all the years they have been going they never once sam Robert Mcnamara making tracks of any kind there.

This week in what some might see as a final doff of the establishment hat, Secretary of State Cyrus Vance moved in for a brief holiday-with his bathing suit.