Smoking may cause nearly one-third of all cancer deaths, the U.S. surgeon general warned yesterday. He released the longest list to date of cancers linked with cigarette use.

For the first time, the annual report from government health officials also cautioned nonsmokers to avoid exposure to secondhand smoke "to the extent possible" because of the potential risk of lung cancer.

"Cigarette smoking is clearly identified as the chief preventable cause of death in our society," said Surgeon General C. Everett Koop, who called it the "most important public health issue of our time." He characterized the report as the "most serious indictment" of smoking that the government has yet made.

Koop noted that when the first surgeon general's report was issued in 1964, the available evidence on cigarette smoking singled it out only as a cause of lung cancer in men and possibly in women. The latest report from the Department of Health and Human Services is the first since then to focus on cancer exclusively.

The in-depth review pinpoints smoking as a "major cause" not only of lung cancer but also of cancers of the larynx (voice box), oral cavity (mouth and upper throat), and esophagus.

In addition, the government now considers it a "contributory factor" in the development of cancers of the bladder, pancreas, and kidney. New studies also suggest an association between cigarettes and cancers of the stomach and cervix, but the data is "insufficient," said Koop, to determine how strong this link is.

If it were not for lung cancer deaths due to smoking, Koop said "the overall cancer mortality would have fallen, reflecting improved diagnosis, treatment and survival times" for other forms of cancer.

While cigarettes are considered the chief culprit, the report says that pipes and cigars are also "causal factors" for lung, larynx, mouth and esophageal cancers. The combination of tobacco and alcohol further increases the risk of cancers of the larynx, mouth and esophagus. And long-term use of snuff seems to play a role in cancers of the mouth.

When deaths from heart disease, chronic lung and respiratory diseases and other conditions are also taken into account, tobacco kills an estimated 340,000 Americans each year.

"If I were a smoker of a pipe, cigar or cigarette and were reasonably intelligent and had read this report, I would long since have quit," said Koop, who quit smoking an occasional pipe a decade ago as a prominent Philadelphia pediatric surgeon.

Even though the evidence is far from conclusive, he said that recent studies of the environmental effects of cigarette smoke on nonsmokers are sufficient to consider this a "public health potential hazard." Two studies found a significantly increased risk of lung cancer in nonsmoking wives of husbands who smoked and the third noted a positive, but not statistically significant, link.

Dr. Edward Brandt Jr., assistant secretary for health, wrote in the report that while the controversy is unresolved, "prudence dictates that nonsmokers avoid exposure to secondhand tobacco smoke to the extent possible." He told reporters that nonsmokers "should avoid being in smoke-filled rooms."

Koop defended the Reagan administration's antismoking educational efforts, saying that despite budget cuts, the department's Office on Smoking and Health had survived.

He also maintained that the federal price support program for tobacco is an "agricultural and economic issue and not an issue concerning public health."

The U.S. Department of Agriculture says the support program has cost about $57 million--far less than any other major farm commodity--since it was started in the 1930s, but interest absorbed by USDA on price support loans has cost an estimated $600 million over that time.

Amidst the string of gloomy health statistics, Koop cited some "encouraging" news on the cigarette front. He said that a new survey shows that daily smoking among high school seniors has dropped from 29 percent in 1977 to 20 percent in 1981.

Koop also said that per capita consumption of cigarettes is at the lowest level since 1957 and overall smoking has declined from 42 percent of the U.S. population in 1965 to 32 percent today.

In his first news conference appearance after a prolonged confirmation process, Koop measured his words carefully but did take issue with the industry-supported Tobacco Institute's contention that there is still not sufficient proof that cigarettes cause cancer. His report, he said, had been checked with the "best scientific minds" both in and out of government.