In the summer of 1967, between college and law school, John Rossi II worked as a laborer unloading asbestos products from trucks at a building supply warehouse in his home town of Utica, N.Y.

Later, he became a young partner in a Manhattan law firm. But his life was cut short by a rare and deadly form of cancer called mesothelioma. He was 33, married and awaiting the birth of his first child when he died in December, 1978.

Scientists at New York's Mt. Sinai School of Medicine subsequently said they found traces of asbestos fiber in his lung tissue. Earlier, researchers there identified asbestos exposure as a major danger in contracting mesothelioma and other occupationally related diseases.

Rossi's widow, Nancy, sued the asbestos manufacturer, Johns-Manville Sales Corp., seeking $10 million in damages. The case was to go to court next month, one of more than 16,500 such suits pending against the parent company, Manville Corp., or its subsidiaries.

But a reorganization filing by Manville under federal bankruptcy laws yesterday threw the Rossi case and others like it into legal limbo.

Most of the people alleging asbestos-related health hazards are shipbuilders, construction and factory workers who came in contact with the commonly used mineral; Rossi's age at death and the short time he was exposed to asbestos make his case unusual.

While each case is difficult to prove, medical experts worldwide increasingly have targeted asbestos as the likely culprit in a variety of illnesses, from several forms of cancer to a disabling lung disorder called asbestosis.

"It appears to be the greatest single source of occupational cancer," the National Cancer Institute's Dr. William Blot said yesterday. In addition to mesothelioma, asbestos has been implicated in an increased risk of cancers of the lung, gastrointestinal tract, larynx and kidney. Smoking compounds the risk in the case of lung cancer, in particular.

Asbestosis, caused by tiny asbestos fibers becoming lodged in the lungs, can mean permanent and life-shortening breathing problems in the victims.

While estimates vary, researchers at Mt. Sinai and other institutions have suggested that more than 10 million people -- and perhaps upwards of 20 million -- may have been exposed to the fibers over the last four decades.

This includes roughly 4.5 million shipyard workers during World War II. But the variety of uses of asbestos, which is resistant to heat and corrosive materials, means that workers in several fields, including auto repair, are at added risk.

While scientists generally agree that asbestos exposure can increase the risk to health, there is less agreement on the amount and length of exposure needed to do so.

A government pamphlet warns that "just one month of working with asbestos can double your chances of getting cancer."

Because the cancers may not show up for 20 or 30 years or longer, it is even more difficult to track. But Mt. Sinai researchers contend that at least 5,000 cancer deaths that could be linked specifically to asbestos will occur annually until the end of the century.

Another group of scientists wrote last year that, for those exposed to asbestos before 1965, about 150,000 additional cancer deaths are predicted, "most of which have yet to occur."

In the meantime, many of today's victims contend that they should have been warned about the hazards. Studies since the 1930s have implicated asbestos in lung disease and cancer, but it wasn't until the early 1960s that the evidence began to accumulate.

A 1960 study of South Africans, for example, linked mesothelioma with asbestos, and research a few years later by Mt. Sinai's Irving Selikoff provided stronger data.

There is some debate about how early asbestos manufacturers became aware of the dangers of their product. Many of the lawsuits, including the Rossi case, charge negligence on the part of the companies in not informing workers about the risk.

"This case epitomizes the entire status of asbestos cases against corporations. It involves the worker's right to know that the material he was working with was dangerous," said Arthur Langer, a Mt. Sinai scientist who discovered the asbestos fibers in Rossi's lungs and who planned to testify on behalf of Rossi's widow.

Yesterday's action left Mrs. Rossi's lawyer "frustrated."

"I feel worst of all for the widow, who watched her husband die a terrible death," said Boston attorney Michael Thornton. "We contend that asbestos caused the death, without any question."

But Johns-Manville lawyer David Gross said just as unequivocally that John Rossi's cancer "had nothing to do with the very brief exposure that he had" to asbestos.

"We were very close" to coming to trial, said a devastated Nancy Rossi. "Because of Johns-Manville, I have no husband, my son has no father."