Mexico's Congress approved a bill Friday decriminalizing possession of small amounts of marijuana, ecstasy, cocaine and heroin for personal use — a measure sure to raise questions in Washington about Mexico's commitment to the war on drugs.

The only remaining step was the signature of President Vicente Fox, whose office indicated he would sign it.

Supporters said the law would let police focus on drug smuggling, rather than on busting casual users. The bill also would stiffen many drug-related penalties: for trafficking, for possession near schools, and for possession of even small quantities by government employees.

Criminal penalties for drug sales would remain on the books.

"We can't close our eyes to this reality," said Sen. Jorge Zermeno, of Fox's conservative National Action Party. "We cannot continue to fill our jails with people who have addictions."

The administration of U.S. President George W. Bush scrambled to come up with a response.

"We're still studying the legislation, but any effort to decriminalize illegal drugs would not be helpful," a U.S. diplomat said on condition of anonymity.

The bill, passed by Mexico's Senate on a 53-26 vote with one abstention, had already been quietly approved in the lower house of Congress and was sent Friday to the president's desk. Presidential spokesman Ruben Aguilar indicated Fox would sign it.

"This law gives police and prosecutors better legal tools to combat drug crimes that do so much damage to our youth and children," he said.

If signed into law, the bill could have an impact on Mexico's relationship with the United States — and on the vast numbers of vacationing students who visit Mexico, often to take advantage of its rarely enforced drinking age of 18.

The bill says criminal charges will no longer be brought for possession of up to 25 milligrams of heroin, five grams of marijuana — about one-fifth of an ounce, or about four joints — and half a gram of cocaine — about half the standard street-size quantity, which is enough for several lines of the drug.

"No charges will be brought against ... addicts or consumers who are found in possession of any narcotic for personal use," the Senate bill reads. It also lays out allowable quantities for a large array of other drugs, including LSD, MDA, ecstasy — about two pills' worth — and amphetamines.

Some of the amounts are eye-popping: Mexicans would be allowed to possess a kilogram (2.2 pounds) of peyote, the button-sized hallucinogenic cactus used in some native Indian religious ceremonies.

Mexican law now leaves open the possibility of dropping charges against people caught with drugs if they are considered addicts and if "the amount is the quantity necessary for personal use." But the exemption isn't automatic.

The new bill drops the "addict" requirement — automatically allowing any "consumers" to have drugs — and sets out specific allowable quantities.

Sale of all drugs would remain illegal under the proposed law, unlike the Netherlands, where the sale of marijuana for medical use is legal and it can be bought with a prescription in pharmacies.

While Dutch authorities look the other way regarding the open sale of cannabis in designated coffee shops — something Mexican police seem unlikely to do — the Dutch have zero tolerance for heroin and cocaine. In both countries, commercial growing of marijuana is outlawed.

In Colombia, a 1994 court ruling decriminalized personal possession of small amounts of cocaine, heroin and other drugs. But President Alvaro Uribe, who is almost assured of re-election next month, wants to change that with a constitutional amendment.

"Allowing the personal dosage of drugs is inconsistent with a country committed to fighting the war on drugs," Uribe said at a campaign stop.

The effects could be significant, given that Mexico is rapidly becoming a drug-consuming nation as well as a shipment point for traffickers, and given the number of U.S. students who flock to border cities or resorts like Cancun and Acapulco on vacation.

"This is going to increase addictions in Mexico," said Ulisis Bon, a drug treatment expert in Tijuana, where heroin use is rampant. "A lot of Americans already come here to buy medications they can't get up there ... Just imagine, with heroin."

U.S. legalization advocates greeted the bill with glee.

Ethan Nadelmann, director of the New York-based Drug Policy Alliance, called it "a very good move," saying it removed "a huge opportunity for low-level police corruption." In Mexico, police often release people detained for minor drug possession in exchange for bribes.