A federal court jury in Norfolk yesterday found the Johns-Manville Corp. guilty of negligence and ordered the nation's biggest asbestos producer to pay $750,000 to the widow of a 55-year-old York-town refinery worker who died of a rare, asbestos-related cancer.

The award, perhaps the largest given the growing number of suits throughout the nation involving abestos as an occupational hazards, was given to Helen A. Dishner, widow of Ira H. Dishner,who died of mesothelioma, a cancer of the tissue lining the lungs, last December. The Dishner suit had asked for $3 million.

During the trial, which began two weeks ago, some attorneys said the Dishner case would serve as the precedent for what would happen in more than 40 other suits - involving more than 120 Tidewater workers asking more than $3000 million in damages - yet to come to trial in U. S. District Court in Norfolk.

Tidewater has beem identified as one of the country's major centers of asbestors-related disease by the National Cancer Institue, which along with the U.S. Department of Health, Education and Welfare, has begun a program to warn workers about the hazards.

Most of the suits filed in Norfolk involve workers who were or are employed at the Norfolk Naval Shipyard. Various studies have pinpointed ship-yards as one of the major sources of asbestors-related disease.

Dishner had worked at the Amocorefinery in Yorktown for 18 years. According to testimony during the trial, he had worked around asbestos material for a number of years, and for some of that period tore off old asbestos insulation when pipes had to be replaced.

The president of the Oil Workers Union local at Amoco testified that he and his coworkers often cut asbestos sheets on the workers' lunch table at the plant.

Dishner's attorneys argued that Johns-Manville failed to warn Dishner of the hazards of asbestos, which is made up of miscroscopically small needle-shaped fibers that can be inhaled into the lungs. Various respiratory ailments, along with cancer such as mesothelioma, have been linked to asbestos for years.

Johns-Manville's attorneys said the company has printed caution labels on its products since 1964, and has been a leader in the asbestos industry in pointing out the hazards of the widely used insulation.

During the trial, Judge Richard B. Kellam ruled that Dishner's attorneys could not introduce evidence of fraudulent concealment. That meant that any negligence would be covered by Virginia's two-years statute of limitations.

One of Dishner's physicians had testified that his cancer was triggered in 1975, two years before he filed suit.

Before the Dishner trial started, the court ruled that the statue of limitations would start after the workers' last exposure to asbestos. Some of the plaintiffs in thecases that have yet to come to trial filed suit more than two years after their last exposure.