Virginia's Supreme Court, in a ruling that could mean millions of dollars for the state's shipyard workers, altered yesterday a requirement that lawsuits against manufacturers of cancer-causing asbestos be filed years before any trace of the disease is detected.

The decision was viewed as a major victory for thousands of shipyard employes in Virginia's Tidewater area, where an estimated 250 asbestos cases totaling more than $300 million in claims are pending.

"This is beautiful -- a real breakthrough," said Melena Barkman of the United Steelworkers of America, which represents yard workers at the huge Newport News Shipbuilding and Dry Dock Co. "A lot of times people don't become aware of it [asbestos-related disease] until they get out of the work environment -- which may be 15 to 20 years."

The decision also drew praise from Virginia textile workers, who expressed hope it would aid in winning compensation claims for bysinosis, or brown lung, an incapacitating disease believed to affect hundreds of mill-workers. The state of Virginia has paid only one workmen's compensation claim for brown lung over the last decade, saying the workers discovered they were ill long after the state's statutue of limitations had expired.

Attorney's for asbestos victims had argued that such an interpretation was unfair because mesothelioma, a type of lung cancer caused by repeated esposure to asbestos, often does not show up until decades after the exposure occurs. The disease is always fatal.

The court, in a case, brought against eight asbestos manufacturers by former shipyard worker Douglas T. Locke, yesterday agreed that a strict interpretation of current rules would require a person to bring suit before he knew he had the disease.

It held instead that the two-year statute of limitations on such claims should begin only after the disease is diagnosed. "There is no right of action until there is cause for action," the court said, "The running of the time is tied to the fact of harm to the plaintiff; it is not keyed to the date of the wrongful act."

Attorneys for Locke, who was diagnosed as having mesothelioma in June 1978 and died six months later, had accused Johns-Manville Corp. and others of negligence for failing to warn Locke of the danger of asbestos or equip him with protective clothing or breathing devices.

Locke had been exposed to asbestos beween 1948 and 1972 while working as an industrial electrician in Newport News, an area that has been appointed in several studies as having one of the nation's highest rates of asbestos-related disease.

John's-Manville, the nation's largest producer of asbestos, was among a handful of companies implicated in 1978 in an attempt to hide evidence about potentially fatal effects of asbestos exposure from millions of U.S. workers. According to documents uncovered in a series of lawsuits, the firm suppressed evidence about potential harm to workers in the face of a rapidly increasing number of legal claims.

Spokesman for the Denver-based corporation yesterday declined to discuss the court's ruling.