While the extent of damage from the Three Mile Island nuclear accident near Harrisburg, Pa., is still unknown legal experts say it likely to result in a maelstrom of lawsuits and perhaps higher insurance costs and utility rates at other reactors.

"There will undoubtedly be a hell of a lot litigation resulting from this," said Prof. Harold P. Greeb, an expert on nuclear power issues.

On Capitol Hill, Sen. Gary Hart (D-Colo.) said, "The big cost here will be cleaning up the plant," now plagued by excessive heat and radiation levels.

According to Hart, the question of who pays for the cleanup-the Metropolitan Edison Co. or consumers-remains unanswered.

Under usual industry practice, maintenance and cleanup costs are generally passed directly to consumers. Hart, chairman of the senate subcommittee on nuclear regulation, said in a telephone interview, "The government has a legitimate interest into looking into those escape clauses" that limit the manufacturers' and utilities' liabilities. "I don't understand the whole theory offered by [Energy Secretary James R. Schlesinger] that the consumer has to pay," Hart said.

The nuclear regulatory commission has not issues estimates of the cost of cleaning up the reactor site.

According to Green, who teaches at the George Washington University National Law Center, another likely area of litigation will be suits by persons seeking monetary damages from exposure to the reactor's radioactive emmissions.

As an example of the kind of suits that may be filed, Green said that persons who have worked at the government's Oak Ridge, Tenn., nuclear facility and who came down with leukemia of Hodgkin's disease claimed it was caused by exposure to radiation.

"Everybody who comes down with cancer or other diseases will be tempted to claim that it came from this accident," Green said.

The American Nuclear insurers, a pool of 140 companies that are major insurers for the nuclear power industry, has minimized the likelihood of suits or claims, John Quattrocchi, ANI's senior underwriter, yesterday said he did not expect suits for exposure to radioactivity.

"My understanding is that you are talking about a couple of chest X-rays," Quattrocchi told a reporter. As for the potential for suits suggested by Green, he said: "it is obvious that we are living in a litigious society . . . You have to balance that out with how many nitrite hot dogs did he [the claimant] eat, how many X rays or how much smoking he did."

ANI has issued $140 million in liability insurance fo the Three Mile Island plant. If damages exceed that, however, up to $340 million would be provided by assessing other nuclear plants throughout the country $5 million per reactor, according to ANI's Carol Dower. This, industry officials said, would be passed on to consumers in their utility bills.

Utilities' efforts to pass through costs resulting from nuclear safety questions are now being challenged.

Following the NRC's recent shutdown of five nuclear power plants, Massachusetts Attorney General Frank Bellotti has opposed Boston Edison's claim that increased costs stemming from the closure of its Maine Yankee reactor can be passed on the consumers.

Under the Price-Anderson Act, $80 million in additional liability can be provided by the government. If that also runs out, any remaining claimants would have no recourse.

In its 22-year history, the ANI has paid $620,000 in claims from accidents, the largests of which was for $330,000.