A supply of the controversial cancer drug Laetrile is being studied and analyzed at the National Cancer Institute in Bethesda in preparation for what could be its first scientific test in cancer patients.

A decison on whether to recommend a federally financed trial at the institute and elsewhere will be made "within weeks," Dr. Arthur C. Upton, the institute's new director, said yesterday.

Upton, named to the job Friday by President Carter, made the forecast during a wide-ranging news conference in which he also said:

"As a voting citizen," he would vote for a ban on smoking in public places as one way to reduce smoking and the cancer death toll.

"As a doctor," he also would advise Americans who want to lessen their chance of getting cancer to avoid "excessive use of alcohol" and "high intake of animal fats" and to "control body weight," since more cancers are found in heavy drinkers, heavy eaters and heavy users of animal fats.

He does not endorse Dr. Linus Pauling's view that a high Vitamin C intake can prevent, as well as help cure, cancer - and also prevent colds - but he said he takes 500 to 1,000 milligrams a day of Vitamin C "on general principles."

He will begin a "critical" examination of the institute's $815 million-a-year budget - 30 per cent of the National Institutes of Health budget - to see whether there should be more stress on finding ways to prevent cancer and less on trying to treat it.

Some critics have been saying the institute pays too little attention to environmental causes of cancer, especially chemicals used in industry. Some authorities think 80 to 90 per cent of all cancers are caused at least in part by environmental exposure.

Upton called the 80 to 90 per cent estimate "a tantalizing figure." But he estimated that Americans' personal habits cause more cancers than industrial chemicals.

Nonetheless, he said the institute "must" speed up the testing of the thousands of chemicals used in agriculture, food processing and manufacturing, and, "to the extent that (doing) this may dicate a change" in the institute's Priorities, "I will respond accordingly."

He paid the Laetrile question much less attention in nearly two hours of questioning. But he made it clear that whether to sponsor a Lacetrile trial - a rigorously controlled test of its value compared to other treatments - could be one of his hardest decisions.

He said there are institute people on both sides of the argument, with "the key issue" now an "ethical question" of "whether a physician should administer an agent" that has shown no value, either in reliable human test or in the animal experiments required before use of other drugs.

"I think the chance that there will be a Laetrile trial is now about 50-50." Dr. Vincent DeVita, the institute's clinical director and one of the main proponents of a Laetrile test, said later.

If there is a trial, it would be conducted in the cancer wards of the National Institutes of Health Clinical Center - or hospital - and at other facilities.

"My own leanings are toward doing a test, even though I think Laetrile is a fraud," DeVita said.