Palo Alto voters put fluoride, the controversial cavity-fighting chemical, into the city’s drinking water in 1954. This November, they may be asked to take it out.

An initiative drive headed by Palo Alto psychologist Susan Willis has gathered 2,543 valid signatures, enough to put the issue on the Nov. 4 ballot, according to City Clerk Donna Rogers.

“We stood out on the street and talked to strangers at supermarkets. I personally got 1,000 signatures,” Willis said. “It was a long winter.”

But on Wednesday, City Attorney Ariel Calonne was studying the question of whether a proposed city measure apparently in conflict with state law could be placed on the ballot. A 1995 state law requires Palo Alto and many other cities to fluoridate their water.

But Jeff Green, with Citizens for Safe Drinking Water, a national organization that fights fluoridation, said the law is not clear-cut. A number of cities have successfully taken anti-fluoridation stands, he said.

The city council is expected to discuss the proposed measure Monday evening.

Willis says her interest in the issue began after she was diagnosed with breast cancer. In attempting to avoid chemicals in her diet, she said, she learned that fluoride can damage bones. That eventually led to an alliance with Citizens for Safe Drinking Water.

Willis and other opponents of fluoridation view the process as essentially poisoning the public water supply. The evidence that it reduces tooth decay is questionable, they say, although fluoridation is still supported by major dental associations.

Even if the city stopped putting powdered fluoride in the water, it might be a short-lived victory for Willis. The San Francisco Water Department, which supplies all of Palo Alto’s water, has plans to begin fluoridation within two years.

And there is yet another legal twist. With many initiative issues, the city council may avoid an election by agreeing to do what the initiative asks. The fluoridation question, however, is different, because the program began with the approval of the voters.

“If the community voted it in, the community has to vote it out,” said Linda Clerkson, a spokeswoman for the city utility department.