Sold by the millions and hailed by advertisers as the nation's best nonlethal crime-fighter, tear-gas spray cans have been characterized in reports by California rape victims and police as ineffective devices that may do more harm than good.

Limited tests conducted by sheriffs' departments in Ventura and Alameda counties, backed by reports from rape counselors in Los Angeles, indicate that the most popular type of irritant spray needs 24 seconds to take effect. Even then, the reports say, it is relatively ineffective against attackers who wear sunglasses or are excited or intoxicated.

Judy Ravitz, director of the private Los Angeles commission on assaults against women, said about 80 women who had the spray cans have reported in the last 15 months being unable to fend off an attacker, because they could not get to the can, could not operate it properly, or found the spray had little effect.

Laurie Stevens, director of a rape hotline in Pasadena, said, "I think it gives people a false sense of security. People think these little cans are going to save their lives."

Stevens said one woman, whose alleged assailant's case is now in court, was raped by a man who broke into her home. She managed to fight him off at first and reach a can of tear gas she kept in the kitchen, but when she sprayed it in his face, "he just laughed at her," Stevens said.

A Fort Worth, Tex., woman sued a tear-gas manufacturer after a burglar, apparently enraged by being sprayed in the face, beat and raped her. The manufacturer disputed her story, but agreed to pay her $15,000 without admitting liability, her attorney, David E. Keltner, said.

Tear-gas manufacturers acknowledge that some products on the market do not work or have misleading advertising, the focus now of an investigation by the Federal Trade Commission. But they say most of the cans, available in all but a few states and the District, can help a potential crime victim escape an attacker if used properly. If people lose faith in tear gas, they add, they will just buy handguns.

Tear gas is a misleading term, though. The irritant found in the spray cans is actually a powder dissolved in a liquid solution and sprayed out in a stream or mist. Manufacturers disagree over which of two kinds of irritant--CS (orthochlorobenzalmalononitrile) and CN (chloroacetophenone)--is more effective.

One of the leading brands, "Paralyzer," available in sports and gun shops in Maryland and Virginia, will sell an estimated 6 million spray cans throughout the country this year, according to Gary Harris, marketing director for its maker, Defense Products Manufacturing Corp. of Phoenix.

It is only one of many brands. In California, one of only two states to require training courses for private citizens who want to buy the devices, 19 different brands are registered. The number of people taking tear-gas training in the state has climbed from 4,986 in 1979 to 311,636 so far this year.

Police and rape counselors complain that women armed with tear gas get the impression that it will actually stop an attacker, when it usually can do no more than distract him briefly. A revised lesson plan about to be added to the California training classes says: "It is important to realize that tear gas does not paralyze."

But few states provide training or regulate advertising for the spray cans. The wrapping of a can of Paralyzer, purchased recently for $5.95 at Crawford International Inc. in Silver Spring, Md., shows a young woman spraying an attacker in the face and standing over him as he crouches over with his face in his hands.

The wrapper says: "The 'PARALYZER' has been editorialized on NBC, CBS, and ABC television, in major newspapers and national magazines, as a precision protective instrument that will instantly stop even a 300 lb. man up to 20 minutes, including individuals under the influence of alcohol and/or narcotics."

Asked if he could prove that claim, Harris cited tests made at Edgewood Arsenal and by the International Association of Chiefs of Police. Neither testing center, however, has tried out the spray in simulated attacks. The Edgwood Arsenal used grenades or blowers, not spray cans, in 1976 to test the irritant used by Paralyzer. An International Association of Chiefs of Police test in 1969 showed a 24-second delay before the same irritant took effect in a spray-can test.

The recent failed assassination attempts on Pope John Paul II and President Reagan show "nothing is 100 percent fool proof," Harris said. He added, however, that the company may print "a brochure that may or may not accompany the product" and warn buyers to run away quickly after spraying their attackers.

A spokesman for the FTC said she could not confirm that an investigation of tear-gas marketing was under way, but several manufacturers said they had been contacted by FTC officials and asked about false advertising claims.

Manufacturers make conflicting claims for their products, but police experts, tear-gas salesmen and government officials here and in Washington say no controlled, scientific test has yet determined how effective the various brands of sprays might be in stopping a determined attacker.

John Woods, an official with the California Justice Department responsible for clearing tear-gas brands for use in the state, said his office tests to ensure the irritant contains the proper chemicals, is not mislabeled and that the spray mechanism operates properly. He said California officials dropped the idea of testing the effectiveness of the spray because there was no way to cover "all the cicumstances" in a potential attack.

The closest to a full field test occurred earlier this year at the Police and Sheriff Academy for Ventura County, just northwest of Los Angeles.

Recruits training at the academy acted as robbers attacking local women enlisted for the test by a production team for ABC-TV's "20/20" that filmed the event. According to Ventura County Lt. Steve Giles, none of the 20 women involved was able to stop her attacker, despite having the spray can ready and managing in many cases to shoot the simulated attackers directly in the face.

The police recruits, who jumped from behind cars or walls, "were able to do whatever they wanted to do, with discomfort, but they were able to do it" even after being sprayed, said academy Sgt. Robert Brooks.

Brooks and Giles said all the women in the test had taken the two-hour training course required in California. Having seen the results, Brooks said, "I wouldn't recommend any of my family carrying tear gas."

He said his department's officers have found tear gas ineffective, particularly with individuals who are extremely agitated or under the influence of drugs or alcohol. "Most officers will use their Mace once or twice, early in their careers, and then not use it again," he said.

In the Washington, D.C., area, Montgomery County police have discontinued use of tear gas and Alexandria police are not required to carry it.

"We found it to be ineffective and unpredictable," said Montgomery County police Cpl. Phillip Caswell. "It would not affect inebriates or demented persons," said Alexandria's Lt. Joseph Hilleary.

Police in Prince George's, Fairfax and Arlington counties and the District still carry tear gas, although Marcia Webb of the Fairfax County police said officers there are warned in training that "it is not effective all the time."