The head of the National Cancer Institute promised yesterday to spend less money on a so-far fruitless search for a cancer virus or cancer vaccine and more research on how diet affects cancer.

This will include the unsettled question of whether fried hamburgers cause cancer, Dr. Arthur Upton, cancer institute director since last year, told a Senate nutrition subcommittee.

He also said the institute would do more to tell people that there is already strong evidence that three types of dietary abuse - over-eating, excess drinking and too many fats in the diet - may lead to cancer.

Upton pledged these actions in response to charges that his institute had spent only one per cent of its budget on dietary research, despite the assertion by subcommittee chairman Sen. George S. McGovern (D.S.D.) and support by some scientists that half of all cancers may be related in some way to what people eat.

"The suspicion that we're losing the war on cancer because of mistaken priorities has grown stronger in my mind as I've listened here today," McGovern said after hearing Upton and Upton's chief, Dr. Donald Fredrickson, director of the overall National Institutes of Health in Bethesda. They spoke for two hours.

"The federal government is not responding to public outcry" for more knowledge about diet and cancer, said Sen. Bob Dole (R-Kan.), ranking minority member.

In reply, Upton conceded NCI failure to do enough on nutrition.

Questioned about the large sums spent on virus research - $100 million this year of NCI's $867 million - Upton said some of these funds would be redirected.

Asked about charges that some NCI officials have been cronies of scientists who received research monies, Upton said he is reorganizing the agency to try to insure an impartial review for all grants and contracts.

He said he named 12 "program working groups" to review all of the institute's plans and priorities. He promised that money for nutritiona research would be increased.

Upton said the current nutrition research figure is "nearly $16 million," and this might grow to $30 million by 1981. But McGovern complained that the institute has given him three different estimates so far of 1977 nutrition spending, so "we can't even get" a clear picture of dietary directions.

As to fried hamburgers - and whether they may help cause cancer, as alleged last month by scientists at Washington University in St. Louis - Upton said any cancer-causing substance in them "is likely to be weak influence," not a strong cause for cancer.

"Certainly an occasional hamburger is something nobody should worry about," Upton said. "As to a hundred hamburgers a day, we just don't know. And to do the research (to find out) is going to be a mighty job."