No one knows whether sodium nitrite in food causes cancer, the General Accounting Office yesterday told seven congressmen who question the idea of a federal ban on the chemical.

The GAO report was the latest shot in a battle that has raged since August 1978. Dr. Paul Newberne of Massachusetts Institute of Technology -- studying nitrite preservatives for the Food and Drug Administration -- said they caused cancer as well as heart, spleen and other disorders in rats.

The FDA and Agriculture Department proposed to phase out the chemical, used to add color and flavor -- and, more important, prevent botulism -- in over two thirds of the nation's pork and a tenth of all beef products.

The phase-out was to be gradual, over several years, as other methods to prevent botulism were developed

The FDA never made a final decision, however. The meat industry and many members of Congress objected. Reviews were begun of the MIT data, and Newberne himself said that, while a gradual nitrite phase-out was justified, there should not be an extensive one without more animal study.

Such study, though it would take another three or four years, has never been started. And yesterday GAO, Congress' auditing agency, told Rep. William C. Wampler, of Virginia, ranking Republican on the House Agriculture Committee, and six colleagues that:

Many scientists in and out of government have raised questions about Newberne's studies, especially the accuracy of his diagnoses of lymphomas, or lymph gland cancers, in his test animals.

FDA did a poor job of monitoring Newberne's studies and allowed many flaws in them.

FDA Inspection of Newberne's laboratory revealed contamination, a feeding mixup and other "serious problems" that may have jeopardized the study's validity.

"Do you mean," asked Rep. James G. Martin (r-N.C.), "that there is no scientific justification for the crusade on which the FDA and Agriculture Department)$ have embarked?"

That is generally "a fair characterization," Ed Densmore, deputy director of GAO's human resources division replied.

Newberne, in letters appended to GAO's report, called his studies valid and said most of the criticisms were characteristic of "those who are unfamiliar with the nature of the problem."

Dr. Donald Kennedy, a highly regarded biologist who headed the FDA until he became provost of Stanford University last year, said at Stanford that food laws required FDA to start planning possible action on nitrite, while taking care to check the Newberne study's validity.

"As to whether" Newbern's finding of lymphomas was statistically valid, said Kennedy, we ordered a slide review which is not yet complete. But the answer to the general question, 'Are nitrites safe? is no," first because the Newberne study did not address all possible ways nitrites are suspected of causing cancer, and second because Newberne's rats showed other health problems.