The office of Mexican President Vicente Fox says he will not sign a bill that would have legalized possession of small amounts of drugs such as marijuana, cocaine and heroin.

President Fox's office said in a statement Wednesday that the law would be sent back to Congress for changes. The statement said in Mexico, the possession of drugs and their consumption "are, and will continue to be, crimes."

The Mexican Senate passed the bill last week, surprising many in the United States. Mr. Fox's office had said he would sign the measure.

Under Mexican law, local police and judges currently decide whether people should be prosecuted for possessing small quantities of drugs.

The bill also would have allowed the possession of small amounts of the hallucinogenic drug, L.S.D., amphetamines and ecstasy.

Some officials had voiced concern the measure could increase drug use by border visitors and U.S. students who travel to Mexico on vacation.

Meanwhile, the White House Office of National Drug Control Policy said in a recent statement that last year, Mexico eradicated 21,600 hectares of opium poppy and 30,840 hectares of marijuana.

Officials say the eradication caused a major drop in the amount of the drugs that would otherwise have headed mainly to the U.S. market.