Surgeon General Julius Richmond yesterday endorsed a switch to "less hazardous" cigarettes for smokers who have difficulty quitting, but warned that no cigarette is safe and switching does far less good than breaking the habit.

Richmond, who is also assistant secretary for health in the Department of Health and Human Services, added many other cautionary notes. And he warned pregnant women against smoking any cigarettes.

Nonetheless, his statement on the less hazardous brands was the main conclusion in an annual report to Congress on progress against smoking. It came at the end of a year-long study of all that is known about the effects of the newer low-tar, low-nicotine cigarettes, which now represent about a third of the market.

A moderately favorable statement about them caused a major flap at the then-Department of Health, Education and Welfare in mid-1978.

Dr. Gio Gori, then deputy director of cancer prevention at the National Cancer Institute, said then that some could be smoked in "tolerable" numbers, say three to eight cigarettes daily, or perhaps several more of a few brands, without "appreciable" ill effects on the average smoker. He said the effects of such light smoking of the 20 or so least hazardous brands would be as small as that of just two cigarettes daily before 1960.

Gori was forced out of the cancer institute, with officials from Hew Secretary Joseph A. Califano, Jr. on down insisting that his view was misguided and would only hinder their efforts to discourage all smoking.

Richmond by no means went as far as Gori.

Specially, Richmond said in his 237-page report, "The Changing Cigarette," that:

There indeed has been a great change in cigarettes, with a third of all smokers, or 18 million persons, now puffing on cigarettes with a tar yield measured at less than 15 milligrams.

There is still no safe cigarette or amount to use.

Smoking the less hazardous cigarette nonetheless "reduces" the risk of lung cancer.

Because there is not enough information yet, "it is not clear" what benefits there will be in avoiding heart or obstructive lung disease (most seriously, emphysema). Cigarettes cause more heart disease deaths then they do lung cancer deaths.

There is no evidence that switching brands has any benefit on fetuses. There is considerable evidence that pregnant women who smoke have more trouble in pregnancy, abort more and bear babies with higher mortality rates, lower weight and more birth defects and other problems.

Switchers to less hazardous cigarettes may cancel any benefit by smoking more or inhaling more deeply. Heavily inhaling smokers swallow more tar and nicotine than official measures of content would indicate.

No one knows, Richmond added, whether the new cigarettes offer new risks by their design, filters, tobaccos or additives, and manufacturers have refused to tell what chemicals they add to help compensate for reduced tar and nicotine flavor.

There is great need, Richmond said, for more "public action" against cigarettes generally, and for more facts about the newer cigarettes.

Backing him, HHS Secretary Patricia Roberts Harris said manufacturers should list the yields of tar, nicotine and other hazardous components on their packages and ads. She endorsed previous secretaries' demands for stronger health warnings, establishment of maximum allowable tar and nicotine levels and disclosure of more information.

Dr. Gori, now a vice president here of the nonprofit Franklin Institute, welcomed the new Richmond statement. He said he thinks it likely that milder cigarettes will cause less disease in general, not just less lung cancer.

"We all agree the best thing to do is quit smoking," he said. "But it is also compassionate and practical to encourage people who can't quit to at least switch to less hazardous products."