Pennsylvania officials said yesterday that they are continuing to fluoridate water near Pittsburgh despite a judge's order there Wednesday to stop adding the fluoride because it may cause cancer.

Allegheny County Common Pleas Judge John P. Flaherty said he based his decision on a study by a pair of blochemists that indicates elevated cancer rates in 10 large U.S. cities where water was fluoridated. The judge's ruling drew an immediate sharp reaction yesterday from some of the nation's leading dental and cancer experts.

Calling the judge's decision "shockingly" Dr. Marvin Schneiderman, associate director of the National Cancer Institute's institute for science policy, said that, of materials to which large numbers of humans are exposed, fluorides have been among the most heavily studied.

"There is no well-done study which shows fluorides to be a risk a humans," Schneiderman said.

Schneiderman and several other medical experts, all of whom testified during nearly six months of hearings on the Pittsburgh lawsuit, said yesterday that the study cited by Flaherty was "seriously flawed."

The research scientists were Dr. John Dean Burk, a former NCI official and Dr. John Yiamouyianmis, a biochemist from Delaware, Ohio. In an interview yesterday Burk said they found a significant difference in cancer rates between two 10-city groups, one of which fluoridated the water.

"We think we have answered the other side's questions," said Burk. "Personally I'm not against fluoride persue. But if you want to save people from cancer deaths them I am against it in water supplies."

Schneiderman said that the study by Burk and Yiamouyiannis did not take account of changes in the population age and sexual makeup of the cities as well as other critical factors.

"It was apparently a wild coincidence," he said, "but the cities they picked which fluoridated their water had populations which were older, while the nonfluoridated cities had younger populations with less likelihood of cancer showing up."

The reason for the difference, he said, may be that many cities that added fluoride were in the northeast where average population age is increasing. Many of the other cities were in the South and West where populations are growing and the average age is decreasing.

Frederick Baxter, attorney for the West View Water Authority, which serves about 160,000 persons in 26 communities north of Pittsburgh said yesterday that it would continue to add fluoride while the case is on appeal to the Pennsylvania Commonwealth Court.

Attorneys for the agency said Flaherty had overstepped his judicial authority in ruling that the fluoridation should be discontinued. Pennsylvania law, they said, gave that power only to the Department of Environmental Resources, which has granted the Agency a fluoridation permit since 1963.

"The real problem," said Baxter, "is we NOW have 160,000 people scared to death based on a report we feel is absolute nonsense. The damaged has been done no matter what happens."