LOS ANGELES, Oct. 29— The Clinton Administration has condemned it as a cynical hoax, the Republican Presidential candidate, Bob Dole, has denounced it as dangerous, and in a letter released today, former Presidents George Bush, Gerald R. Ford and Jimmy Carter call it a threat to the public health of ''all Americans.'' 

But in the battle over Proposition 215, the California initiative that would legalize the medical use of marijuana for people with AIDS, cancer and other diseases, polls show voters leaning away from politicians' dire warnings and toward the likes of Anna Boyce, a 67-year-old nurse shown in television advertisements that began appearing this week. 

Describing her husband's death from cancer, she tells viewers: ''The nausea from his chemotherapy was so awful it broke my heart. So I broke the law and got him marijuana. It worked. He could eat. He had an extra year of life. Proposition 215 will allow patients like J. J. use of marijuana without becoming criminals. Vote yes on 215. God forbid someone you love may need it.'' 

Three recent California polls show a majority siding with Mrs. Boyce and Proposition 215, which would require only a ''doctor's recommendation'' for marijuana use by patients with AIDS, cancer, glaucoma ''or any other illness for which marijuana provides relief.'' 

A Field Poll ending Oct. 9 showed that 56 percent of those surveyed would vote for the measure, a private poll in the same period by the campaign for Proposition 215 found 57 percent supporting it, and a Los Angeles Times poll released last week found 58 percent in favor. The opposition never topped 36 percent in the three polls. 

Advocates of tough drug policies are deeply concerned, seeing before them the prospect of a precipitous loosening of control over marijuana use in the nation's most populous state. 

''We believe the vote of Californians on Proposition 215 is the most important vote they will cast in the 1996 elections,'' said Joseph A. Califano Jr., the former Secretary of Health, Education and Welfare who founded the National Center on Addiction and Substance Abuse at Columbia University. In terms of drug policy nationwide, he added, the vote on 215 is ''unquestionably the most important vote that will be cast in this election,'' particularly because California has been a trend-setter on social issues. 

The public support for Proposition 215 highlights a shift in public opinion: even the initiative's foes acknowledge that people are siding ever more decisively with the idea that seriously ill patients should have access to anything that will ease their suffering. 

A poll commissioned by Mr. Califano's center found that 58 percent of Californians said marijuana should be available to the dying. 

But Gen. Barry R. McCaffrey, President Clinton's drug policy director, complains that the initiative goes much further than help for the dying. He issued a strongly worded statement today, calling 215 a ''falsely labeled, cynical initiative.'' 

National medical groups have refused to endorse marijuana treatment, he said, adding that the initiative was actually a ''stalking horse for legalization'' because it did not specify that a doctor's prescription be written. It would also send the message to teen-agers that ''marijuana is medicine,'' he said. 

''We should ask ourselves whether we really want Cheech and Chong logic to guide our thinking about medicine,'' General McCaffrey said. 

Mr. Califano's group, which researches drug abuse and seeks to promote public concern over it, on Monday released the results of its own poll, which showed that Californians' support for the initiative had dropped to just 46 percent. 

But proponents of the initiative immediately dismissed the survey as a flawed poll that prompted negative results from respondents and deviated too much from others to be credible. They also objected to opponents' warnings that the initiative would open the door to virtually a blanket legalization of marijuana. Patients in Florida and Ohio already have protections similar to those that 215 will provide, they say. 

''At a certain point, the other side needs to stop trying to scare people and confuse voters, and we need to start thinking seriously about how this is really going to work in California,'' said Dave Fratello, a spokesman for the pro-215 campaign, which held its own news conference immediately after Mr. Califano's. 

General McCaffrey is not ready to contemplate any such thing. He plans to spend three days in California working with the local police and elected officials to fight the initiative. 

A force against the initiative is the mounting alarm nationwide over a recent doubling in marijuana use among teen-agers and voters' concern, as found in the poll sponsored by Mr. Califano's group, that Proposition 215 would lead to increased recreational use of marijuana. 

But in its favor there is public sympathy for people like Judith Cushner, a former breast cancer sufferer who described on California television how marijuana had helped her through the pain of chemotherapy. She warned, ''Someday, you may need it.'' In another advertisement, Dr. Richard Cohen, who has defied California law and prescribed marijuana for many cancer patients, says, ''Morphine works. Marijuana works. Let us physicians treat you with every medicine that can help.'' 

Backers of the initiative have $750,000 to spend on such commercials in the week before the election, Mr. Fratello said. Opponents have managed to raise only $30,000 overall, leaving them fuming that they have been hobbled by the lack of money for advertisements and that denunciations by politicians like Gov. Pete Wilson and Senator Dianne Feinstein are not enough. 

''We've been telling people for months that the only way to stop this is to send some money and let us get on the air,'' said the manager of the campaign against 215, Stu Mollrich. ''And nobody's done it.''