Lloyd's of London Chairman Peter Miller today announced an "inquiry" into why one of its underwriting agencies has suffered unprecedented losses of up to $165 million, but said there will be no "financial lifeboat" to rescue the hundreds of Lloyd's investors who are liable for the bill.

In a general meeting with investors and later with reporters, Miller staunchly, and sometimes heatedly, defended Lloyd's reputation and ability to offer "one of the strongest policies of insurance in the world."

Overall, he said, the Lloyd's insurance market expects to record a profit, due primarily to investment profits balanced against underwriting losses, of about $64 million for 1982, the year for which the market's books have just been closed.

Lloyd's accounts are tallied three years in arrears because of delays in settling claims.

Miller announced several steps taken by the Lloyd's governing council in response to the loss, including appointment of a new, independent agency to handle the investors' affairs; the naming of a separate inquiry committee, without a disciplinary mandate, to "establish facts" about the losses, and the establishment of another committee to advise investors.

Miller's assurances are likely to provide little comfort to the losing investors, however. Many of them have threatened to hold up payment of losses and to take legal action against what they charge have been unsound practices by underwriters that Lloyd's should have been aware of and acted to prevent.

Today's meeting was the latest chapter in a long-running controversy that has called into question the reliability of the 400-year-old institution whose name long has been synonymous with insurance.

Although the underwriting losses reflected are the largest in Lloyd's history, they involve only a small percentage of Lloyd's thousands of investors, who are called members, or "names." They revolve around only one of the hundreds of underwriting "syndicates" through which the investors channel their money.

"It is not correct to argue from the particular to the general and to stigmatize Lloyd's as an institution that cannot be trusted," Miller said today.

But the controversy reflects an overall concern that Lloyd's, which in 1982 was granted special self-regulatory powers by an act of Parliament, must either better police those who do business under its market umbrella, or be subject to outside regulation.

It began last year when directors of one of the underwriting agencies operating at Lloyd's, known as the PCW Agency, were accused of fraud and having used investors' money for their own private business and pleasure. A total of about $50 million was lost.

The investment syndicates operated by the agency were placed under the control of another, the Richard Beckett Agency, and the losing members were reimbursed, although no interest was paid. Lloyd's took no action against the principal alleged thief, saying that it had no standing in a matter that was up to government prosecutors. He has since left the country, and no charges have been brought.

In April, however, Richard Beckett announced that the same syndicates had suffered enormous underwriting business losses, because of what Miller today called "the utterly disastrous results of large sections of the American casualty book." Many of the syndicates' policies involved U.S. product liability in areas, particularly asbestos, where U.S. courts have awarded heavy damage awards.

While they must place only a portion of their assets on deposit, investors at Lloyd's are liable to the full extent of their personal wealth. For some investors in the losing syndicates, this will mean bankruptcy.

According to Lloyd's, which only provides the marketplace in which the underwriters operate, this is unfortunate but unavoidable. "Trading as we do on the basis" of an unlimited liability, Miller said today, "there will always be, as there always has been, a possibility of financial disaster from underwriting losses."

For many of the affected investors, however, the possibility of coincidence between last year's fraud and this year's business losses is too great to ignore. A number of them have formed a committee and sought independent accounting and legal advice.

On the basis of this advice, some of them have said they may refuse to meet Lloyd's "cash call" -- the process through which they must demonstrate that they have sufficient money to pay off the losses their syndicates are expected to incur.

The members maintain that, until a complete investigation is carried out of whether the additional losses incurred this year also involved some sort of fraud, they should not be required to pay.

Miller said today that "it would be no part of the council's policy to drive any person finally into bankruptcy who makes a genuine attempt to meet his full obligation."

But, he said, the deadline for investors to demonstrate solvency is July 31. If any of them "can't or won't," he said, policy claims will be covered out of the Lloyd's Central Fund, and the investor will be suspended from membership.

If the investors take action against Lloyd's, he said, "we will stand up to litigation, and the law will tell us what we must do."

The question of whether Lloyd's would take legal action against the investors, Miller said, was up to "the judgment of the council."