Saccharin is not as great a danger to most adults as some scientists believed a few years ago, but it is a possible cause of bladder cancer for some, especially heavy users and users who smoke, the National Cancer Institute said yesterday.

In an attempt to settle the long-standing controversy over the widely used artificial sweetener, NCI spent 16 months in 1978-79 interviewing more than 3,000 bladder cancer patients and 6,000 healthy people about their dietary habits.

The $1.5 million study, according to preliminary results released yesterday, did not find the 60 percent increased risk of bladder cancer in saccharin-consuming human males that was found in Canadian research that was regarded as the most complete such study until now.

In fact, the NCI study found "no increased risk" in the overall study population. This still does not mean no risk because even this population was not large enough to detect any occasional sweetener-caused bladder cancer that add could up to thousands of cancers in millions of people.

The NCI scientists did say that:

If there s any increased risk to men in genera from "average" consumption of artificial sweeteners such as saccharin and cyclamate -- and animal studies indicate there may be -- it is probaby no more than 18 percent.

Heavy users of artificial sweeteners, especially those who consume diet drinks and other sugar substitutes, showed a 60 percent increased risk of bladder cancer. "Heavy use," in the study language, means six or more servings a day of a sugar substitute or two or more eight-ounce diet drinks.

Heavy cigarette smokers -- men who smoked two or more packs daily or women who smoked one or more -- who also used artificial sweeteners heavily showed a higher risk of bladder cancer than heavy smokers who shunned the sweeteners. The scientists could not put a percentage on this increased risk.

Bladder cancer is normally three times more common in men than in women. But women who consumed sugar substitutes or diet drinks twice or more daily had a 60 percent greater risk of developing this form of cancer than did other women.

A "60 percent excess risk," NCI explained, means that where women who don't use artificial sweeteners have an estimated yearly rate of five cases of bladder cancer per 100,000 women who consumed the sweeteners twice or more daily would develop eight cases a year per 100,000.

The study did not address the question of consumption of artificial sweeteners by children, or how many of today's children who consume diet drinks will become tomorrow's cancer patients.

Dr. Jere E. Goyan, the Food and Drug Administration commissioner, said yesterday "this study is consistent" with previous animal studies and scientists' conclusions "that saccharin is a weak carcinogen," or cancer causer and is a cancer promoter in conjunction with other causes, like cigarette smoking.

He said, "I reiterate my concern about consumption by so many Americans, especially young people, of large amounts of saccharin. We may have to wait 20 or 30 years to assess the possible effects on our young people," since they are consuming far more artificial sweeteners than the adults in the study consumed.

But Goyan said "we'll do further analysis of the data" and "consider our options" before any renewal of FDAs proposal to ban saccharin except in table-top sweeteners for dieters and diabetics.

Congress enacted an 18-month moratorium on any ban.It expired in May. The House has passed a new, two-year moratorium, but the Senate has not acted.