Two New Yorkers who say they invested $192,000 in an Iranian copper mining concession are suing the Tehran government for $450 million to compensate for the seizure of their interests and the loss of the fortune they say they would have amassed there.

The suit, brought by William Bikoff and George Eisenpresser, was filed Oct. 6, almost one month after Ayatollah Ruhollah Khomeini declared that cancellation of all claims against Iran was one of the four conditions for release of 52 Americans held hostage in that nation.

The Bikoff-Eisenpresser claim is the largest of 318 lawsuits against Iran, the settlement of which has become one of the major sticking points in reaching agreement on the hostage problem.

The $450,192,000 claim is based on valuations by "geological experts" of the "hundreds of millions of tons of high-grade copper" contained in their concession area, according to papers filed in U.S. District Court in Washington, D.C.

Efforts to locate either of the two claimants or to obtain information about their mining company were unsuccessful. Three present or former top executives of the Anaconda Co., which in 1971 was selected as technical consultant to the Iranian government to develop the vast Sarcheshmeh copper reserves near Kerman, said they had never heard of either the New Yorkers or their company.

State Department officials also said they were unfamiliar with the company and were unable to pinpoint the geographical location of Naghsag Gooshe, the stated site of the New Yorkers' mining concession.

In one of the ironies of the tense hostage situation, American claims against the more than $8 billion in frozen Iranian assets began to pour in after Khomeini's terms for the hostages' release were made known Sept. 12 and later approved by the Iranian Majlis (parliament). According to the Philadelphia-based newsletter, The Iranian Assets Litigation Reporter, 60 have been filed since Nov. 1.

Both U.S. and Iranian officials have since begun to raise questions about the size of these claims, now reportedly totaling nearly $7 billion.

"There is water in some of them," a U.S. Treasury official said recently.

As an example, one official noted that the Dupont Co., in its $96 million claim against Iran, included a $10 million in "anticipated dividends" and $19 million more for "loss on equity" -- all based on a $43 million investment in a synthetic textiles plant in 1974.

The governor of Iran's Central Bank, Ali Reza Nobari, said in a recent telephone interview from Tehran that he believed many of the claims were "questionable."

What helped spawn the rash of legal actions were statements by U.S. officials giving assurance that legitimate U.S. claims against Iran would have to be met -- either through the courts or through a settlement commission.

That view has been echoed by Iran's Nobari, who last month suggested that an international commission could be established to settle claims, and that Iran would put several billion dollars in escrow to cover any awards.

Nobari, however, also recently raised for the first time the possibility that Iran, in any claims tribunal, woudl seek to determine if the companies or individuals had obtained their contracts corruptly through bribes or had failed to pay the required taxes during their operations in his country.

Over the last few years, U.S. companies have filed about 600 disclosures with the Securities and Exchange Commission admitting they made questionable payments in dozens of foreign countries, including Iran. But the firms assert that doing business in Iran was risky and frustrating and that they operated according to local business customs.

The Bikoff-Eisenpresser suit involves an Iranian company formed in 1970 by the two Americans and four unidentified Iranians. Each partner got one-sixth of the Zarshouran Mining Co.

The company, according to an affidavit by Bikoff filed with the suit, received on June 6, 1973, an "exploitation license covering an area of approximately 40 square kilometers called Cheshmeh Shirin in the heart of the copper-rich area of Naghsag Gooshe."

The exploitation license according to Bikoff's affidavit, "was the last one to be granted to a private enterprise" and was to run until June 25, 1988. oIt permitted the company to "sell and export the minerals and retain all profits."

Bikoff, who described himself as "managing director" of the company, said five years were spent surveying the site, constructing mining camps, digging trenches and bringing in geological survey teams from the United States, France and Germany.

All this, according to Bikoff's affidavit, cost the two U.S. partners $192,000.

As for the concession's worth, Bikoff's affidavit said, "I have been informed by geological experts that under normal methods of valuation, the value of the one-third interests of [himself and Eisenpresser] in Cheshmeh Shirin is not less than $450 million."

Bikoff described the $450 million he and Eisenpresser seek as "justly owed . . . by Iran and there are no offsetting claims which could be asserted against us."

Bikoff according to his New York lawyer, "does not want to talk about this." His colleagues at William Bikoff & Associates refused Friday to disclose his whereabouts and also declined to describe the activities of the firm. One associate, Herb Charles, said, "I didn't know anything about the Iran suit until I read about it."

Attempts to locate Eisenpresser were also unsuccessful. His wife, contacted at their Floral Park, N.Y., apartment, said she would take a message for her husband but would not say where he was or when he would return.

"I've never heard of these people or their companies and neither have our lawyers," said Ralph Cox, Anaconda's president. Anaconda, which spent an estimated $12 million in Iran in the 1970s, has not filed suit against the Iranian government but has advised the Treasury Department that it might have a future claim.

Several Iranian and American businessmen said the existence of a concession providing for private exploitation of mineral rights was a surprise in light of the Iranian government's post-1971 policy of placing copper development in the hands of state enterprises. In the case of the rich Sarcheshmeh reserves, the government purchased the concession from the Rezais, a wealthy Iranian business family now reported to be living in western Europe.

Despite this policy, Cox said, he received overtures from Iranian attorneys now and then suggesting that Anaconda enter into private deals to develop copper areas.

As Bikoff noted in his affidavit, "exploitation licenses were rarely, if ever granted by the Iranian government." The suit did not identify the Iranian partners who maintained a controlling two-thirds interest in the private Zarshouran concession.

Bikoff's affidavit said that when "civil unrest started and escalated sharply in Iran, several work stoppages struck [his company]."

Shortly thereafter, the company shut down and on Nov. 17, 1979, "all major mines were nationalized."