The name Magellan Petroleum hardly ranks among America's corporate giants. Until the last fortnight, when its affairs occupied three separate full-page advertisements in the Wall Street Journal, few investors can have even known or cared of its existence given its bleak record of 23 successive years of losses.

But Magellan's tangled affairs provide an instructive guide to the changing business ethics that are becoming commonplace in President Reagan's Washington.

The company is largely controlled by America's most prominent family of the New Right -- the Buckleys. Among the family members are former senator James Buckley, who is now under secretary of state for security affairs, and William Buckley, a newspaper and television commentator and a regular on Reagan's dinner guest list.

A rebel group of Magellan shareholders, led by Canadian-based United Canso Oil and Gas Co., is seeking to dislodge the Buckley family. In their message to shareholders, the oilmen have noted that the Securities and Exchange Commission is currently investigating certain companies associated with members of the Buckley family, particularly Catawa Corp., which they control. As a result of these investigations, the SEC has informed Magellan that it will soon be seeking remedy through the civil lawsuit.

Whatever the merits of the Magellan case, it seems that the New Right has a different view of business ethics and regulation from that of the more moderate Republicans and Democrats who have dominated Washington thinking in recent years.

The change in attitude has been on full public view in recent days. Stanley Sporkin, who in his 20 years as SEC enforcement chief had earned the reputation as the toughest policeman around, abandoned ship in the face of New Right resentment and became general counsel to the CIA, where his investigatory talents were likely to be more appreciated.

Despite a Senate furor over the nomination of Ernest Lefever as assistant secretary of state for human rights, the Reagan administration for an extended time persisted in his defense. At issue in the Senate was not so much Lefever's view of human rights but the ethics of donations to a center he directed from the milk formula lobby.

Two other examples of the changing ethic spring to mind. President Reagan seemed to see nothing wrong in the behavior of his son, Michael, who invoked his father's name to try to secure government defense contracts. Yet under the now abandoned code of conduct introduced by his predecessor, Jimmy Carter, after his brother Billy's dealings with Libya, such behavior would have been specifically forbidden.

Second the White House appears to have decided that bribery by American companies is not such a bad thing after all. After the Carter team spent the last few years trying to bully its friends, including Britain, into a tougher code to prevent international bribery, the United States under Reagan believes that export business comes first.

The theme that connects this series of apparently unconnected events is the New Right's antipathy to regulation of business of any kind and international regulation in particular. Although it might clearly be possible in pure balance-sheet terms to show that regulation stifles initiative and in some cases profits and dividends, it does not address the abuses that created the necessity for such rules in the first place.

The United States, which has been in the forefront of corporate regulation, is abandoning its leadership role in the pursuit of short-term gains.

There can be little doubt that the SEC has been the glittering light over the years in the bureaucratic wasteland that is Washington. As Sporkin said: "We've helped preserve the integrity of our markets. That has made the U.S. markets safer than any other markets in the world."

It is a scandal that more information on British companies is available in the United States through the SEC's tough disclosure rules than in Britain. It is also worth nothing that on many occasions in the United States the threat of litigation alone is enough to bring the errant companies to heel.

Nowhere was this more clear than in the case of international business bribery that erupted in the mid-1970s. Although the Reagan administration, in the hope of improving America's export performance, has taken aim at the Foreign Corrupt Practices Act, it was not the act, but the threat of legal action that led to disclosure statements by so many companies -- including British firms.

Institutions and laws such as the Corrupt Practices Act have established a certain moral authority for American business after the dark days of Watergate, Vietnam, and ITT intervention in Chile.

The New Right appears to believe that by adapting ethical standards to allow unscrupulous businessmen to plunder investors, multinational companies to plunder governments they dislike, salesment to corrupt foreign government officials and the president's family to trade on its name, they will unlease a competitive spirit in the American economy that has been lacking in recent years.

It is an assumption that must be challenged. Despite the burden of regulation, compounded by sky-high interest rate imposed almost by government fiat, business appears to be doing very nicely. Gross domestic product is up by 8.4 percent in the first quarter.

If Congress eases the Foreign Corrupt Practices Act, and a bribery row with an oil supplier erupts or the SEC fails to prevent a share-dealing scam, it will be only a short time before clamor for tough regulation will again be heard all the way to the White House. So why needlessly change the rules in the first place?