Hundreds of wealthy investors -- and some not so wealthy -- are being held liable for as much as $165 million in the biggest loss in the 400-year history of the Lloyd's of London insurance market.

The loss comes close on the heels of a series of scandals and fraud investigations that have rocked the staid institution known the world over for insuring everything from the largest ships at sea to satellites in outer space.

It stems largely from policies written through Lloyd's and held in the United States, in precisely those high-risk areas that have meant the recent ruin of similar groups of U.S. investors -- medical malpractice, asbestos poisoning and general product liability -- through escalating claims and court judgments.

Some of those affected, who include Saudi Arabian entrepreneur Adnan Khashoggi and the duchess of Kent, are likely to be able to absorb the loss. The average liability is estimated to be about $250,000, but it could go much higher for many, depending on the extent of their investment and wealth, and could mean bankruptcy for some members. Initial payments on the debt must be made by July.

Despite its sophistication and eminence, Lloyd's today is based on the same operating principle as when it began in Edward Lloyd's London coffee house in 1688. A gathering spot for seamen, it was also a center of information on sailings and cargos, and a center for the writing of insurance.

A merchant with a ship to insure would, through Lloyd's, offer subscriptions among the wealthy. In exchange for a portion of the premium, these investors would agree to meet their share of a claim to the extent, if need be, of their entire personal fortunes. That principle still applies.

To invest through the Lloyd's marketplace today, an individual must show easily accessible assets of at least 100,000 pounds ($127,000), 35 percent of which must be deposited to cover possible losses. Having passed the "means test," an individual member joins one or more syndicates of investors, which in turn are managed by an underwriting agency.

In a meeting here last week with several hundred of the investors involved, an official described as "heart-rending" letters he had received from investors facing financial ruin. "I have been asked in some cases about the technicalities of bankruptcy," said Graham White, managing director of the Richard Beckett Underwriting Agency.

The Beckett agency manages a handful of the more than 400 syndicates that make up the total Lloyd's investment pool. In what Lloyd's officials have described so far as coincidence, Beckett is the agency that took over, in 1982, from another group of underwriting managers who later were revealed to have misappropriated nearly $50 million in investors' funds in 1981.

While much of the money was recovered, the bulk of it was used to pay off underwriting losses. News of the new losses, which come from 1982, and from projected 1983 and 1984 Beckett accounts under Lloyd's three-year auditing cycle, is a further heavy blow to syndicate investors who thought their problems were over.

More than 1,500 Lloyd's members belong to Beckett syndicates, although only about 400 of them are likely to be affected by the new loss.

The full extent of the loss still is not known. "So much is dependent on court awards and the somewhat generous nature of American juries," said David Larner, head of Lloyd's information department.

In recent years, some syndicates got rich, or richer, in the American liability market as high interest rates brought big dividends on invested premiums. Others, who exercised what Larner called "bad commercial judgment" and were hit by massive adjudicated claims, went bust.

Beckett will not say on which accounts the money was lost, although it is believed that the agency took a heavy beating on those involving asbestos poisoning. Beckett official Christopher Tate said only that "from 1973 to 1982, American liability contributed more than 50 percent to the total premium volume of Syndicate 918," one of several syndicates involved.

According to U.S. manufacturers and insurers, more than 30,000 asbestos-related suits have been filed. The fewer than 4,000 settled have cost about $1 billion so far.

"I am able to say this," Tate added. "As a general class of business, with the benefit of hindsight, it is difficult to make" a profit. "The results from American courts have had a disastrous effect on these underwritings." Beckett has announced it will go out of business at the end of the year.

It remains unclear if Lloyd's will show an overall profit in the 1982 audit of its combined syndicates. "We're not going to make much of a profit, if at all," said Larner. Overall losses have been recorded only twice since 1948. Profits for 1980 totaled more than $330 million.

But the magnitude of the Beckett syndicates' losses doubtless has weakened the blue-chip quality of what is considered one of the world's best investment oportunities.

Profits accrue for members not only in interest on the deposited funds, but also through dividends on invested policy premiums. "You put your fortune at risk," Larner noted, "but you get paid twice."

The funds are managed through underwriting agencies such as Beckett, and Lloyd's itself takes no responsibility for the profits or losses of investors.

Lloyd's maintains a special Central Fund to cover those losses the members cannot meet after exhausting their resources. "The most important thing, from Lloyd's point of view, is that these things do not in any way affect policy holders," Larner said.

Under new parliamentary rules and other pending reforms, Lloyd's has begun to take on new responsibilities for the regulation and discipline of those who use its clearing halls.

But players in the lucrative Lloyd's market can expect little sympathy.

"Wasn't it your President Truman," Larner noted, "who said, 'If you can't stand the heat, get out of the kitchen'?"