Will America's most famous fugitive ever be returned to this country to face trial?

For several years now, 41-year-old Robert Lee Vesco has been flicking off criminal indictments, subpoenas and private lawsuits like so many pesky mosquitos as he seeks to fade into the lush background of his Costa Rican redoubt.

But recently there was a change in that country's extradition law which made Vesco suddenly vulnerable.

It remains to be seen whether the Carter administration will push harder than its predecessors for the return of the fugitive financer. As one U.S. offical, formerly based in Costa Rica, puts it: "The Costa Ricans are a little confused because the U.S. has never given them a clear signal that it wants Vesco back."

Adding a measure of immediacy to the Vesco situation is that in June he becomes eligible for Costa Rican citizenship. If granted, it effectively would rule out extradition from that country.

The son of a Detroit auto worker, Vesco gained noteriety in 1970 when he used his modest-sized New Jersey electronics company to take control of giant Investors Overseas Services, Ltd.

Then a $2.3 billion financial conglomerate of banking, insurance, real estate, and mutual funds, Swiss-based IOS was the creation of supersalesman Bernard Cornfeld.

Plublicly, Cornfeld demounced Vesco's heavyhanded takeover of IOS, but privately he sold out his interest in IOS to Vesco for $5.5 million. Indeed, the real losers in the Vesco takeover were the tens of thousands investors from all over the world who put their money behind IOS.

In 1972, the Securities and Exchange Commission charged Vesco with stealing $224 million of IOS's assets. In an attempt to quash the SEC probe, Vesco allegedly made a secret $200,000 cash contribution toward President Nixon's reelection.

This led to criminal indictments by a federal grand jury in New York City of Vesco, former Attornet General John Mitchell and former Commerce Secretary Maurice Stans.

Vesco's accused coconspirators, Mitchell and Stans, were acquitted of the charges in 1974. The U.S. prosecutor bitterly blamed the verdict on the absence from the courtroom of Vesco, the third defendant in the case. Government attempts to extradict Vesco from the Bahamas and Costa Rica were unsuccessful.

For a time, Vesco considered settling in Nassau whose trouble economy welcomed his money. But soon he found that Prime Minister Lynden O. Pindling and his friends began treating the most wanted financier as a captive source of capital for their personal ventures.

Vesco decided to move on to Costa Rica, where he was friendly with then President Jose "Pepe" Figueres. Vesco invested in a troubled business owned by the Figueres family.

Before he completed his term of office in 1974, Figueres got a complaint legislature to pass what became known as the Vesco Law. It said that the final decision on all extradition requests rested with the president.

Figueres was succeeded by Daniel Oduber, but it wasn't until last December that the Costa Rican legislature repealed the Vesco Law, returning decisions on extradition to the courts.

In San Jose, the U.S. Embassy says it has not heard of any new extradition attempts, but expects the Carter administration to take a while getting around to Vesco. Robert Fiske, the U.S. Attorney for the Southern District of New York, where Vesco was indicted, will not say whether his office will try again soon to extradite Vesco.

Meanwhile, the SEC continues to build its huge and complex case against Vesco and his associates. Just about every week, Gregory C. Glynn, a young SEC attorney, travels to New York City to take yet another deposition. The case is expected to go to trial late this year, five years after the commission first sued Vesco.

Not long ago, Glynn flew to Costa Rica to depose a Vesco associate. "I bumped into Vesco at a restaurant," says Glynn, "to our mutual shock."

According to special correspondent Stephen Schmidt in San Jose, Vesco continues to spend lavishly to secure his nest. Vesco is widely believed to have invested $60 million in the economy, and a State Department observer notes, "It cost him money every day to stay there."

Vesco says he plans major investments in the country's Atlantic zone, whose black population, made up of descendants of Jamaican slaves imported to work on the socalled banana railroad, have long felt neglected by the central government in San Jose. One town there was so taken with Vesco that the local football team was named after him.

Vesco, through a foundation administered by his wife, Patricia, donated $120,000 last year to the municipality of Santa Cruz, where he maintains a farm. Not surprisngly, the locals stoutly defend their benefactor.

A Vesco spokesman claims that the financier gets thousands of letters requesting help at his officehome compound located in a suburb of San Jose.

Vesco is so entrenched in the Costa Rican business scene that some businessmen believe his departure could upset the economy. But it is virtually impossible to pin down exactly what he owns. Under Costa Rican law, Vesco can hold bearer shares in companies without his name showing up on the books.

Vesco's interests reportedly include a newspaper, a TV and a radio station, numerous parcels of real estate, and several millions dollars of government bonds.

Patricia Vesco may have helped her husband's status as a member of the community by bearing him a child on Costa Rican soil. Patrick Vesco was born on Nov. 13 and, under local law, is a Costa Rican citizen.

Donald Nixon, the former president's nephew and a Vesco sidekick, followed his leader and kept a low profile in Costa Rica, as have Vesco's other aides who followed him into exile such as Norman Le Blanc, Gilbert Straub and Ulrich Strickler.

Vesco often eats at one of several Italian restaurants in San Jose, his arrival announced by his sleek new Mercedes Benz and four land Rovers carrying his bodygaurds. He appears genuinely afraid that U.S. agents or someone else is out to assassinate or kidnap him. He repeatedly has accused the U.S. Embassy of having a special person in charge of tracking his whereabouts, a claim that U.S. authorities deny.

But an abortive scheme, hatched last year by the U.S. Attorney's Office in New York and labeled by State Department observers as "stupid, dumb, ridiculous," lent credibility to Vesco's claims.

A former convict named James W. "Skip" Wilkins persuaded the government attorneys to pay his way to Costa Rica to spy on Vesco. No sooner had Wilkins made contact with Vesco than be was arrested by machinegun-toting Costa Rican police and thrown into jail.

Later, Wilkins began spreading the word that he actually had been sent to assassinate Vesco. The fugitive has gotten a lot of mileage from this episode, much to the chagrin of U.S. authorities.

Not only does Vesco face criminal and civil litigation from the U.S. government, but also from many foreign governments where IOS did business. There are also countless private suits brought by IOS investors. Nearly $140 million of the $224 million he is accused of stealing reportedly has been frozen in foreign back accounts pending the outcome of the many lawsuits.

One suit was filed by Carlos Recnhitzer, a 77-year-old architech living in Costa Rica. Rechnitzer, who carried around a 5pound lead pipe wrapped in architectual drawings, claims he lost $224,000 in IOS. The week before Christmas, Vesco countersued Rechnitzer, accusing him of slander and libel.

The architect had been quoted by La Republica, a morning newspaper in San Jose, calling Vesco a "crook" and saying he had been "convicted" in the U.S. Rechnitzer said an error in translation caused him to use "convicted" instead of "indicted."

Meantime, as the 1978 national elections approach, the question of whether to extradite Vesco or to give him citizenship is sure to become an issue.

Vesco's friend, former President "Pepe" Figueres, told a Mexican newspaper that Vesco had given money to all the political parties in Costa Rica. It is not surprising that all the parties denied it since it is a violation of that country's constitution for a foreigner to become involved in local politics.