The Bush administration has been vocal in cautioning Canada that Washington would be forced to increase time-consuming border searches if decriminalization of marijuana is enacted. American officials say decriminalization would increase supplies and trafficking.

Canadian officials argued today that the legislation would modernize law enforcement approaches to a drug whose use is often overlooked by the local police.

"I want to be clear from the beginning, we are not legalizing marijuana and have no plans to do so," Justice Minister Martin Cauchon said. "What we are changing is the way we prosecute certain offenses of possessions. We are introducing alternative penalties."

Under the legislation, possession of up to 15 grams — about 20 cigarettes — would be an offense punishable by a fine of up to $180 for youths and $290 for adults. But maximum sentences for illicit growers would increase, and the government would spend about $150 million on an educational campaign to convince young people not to use drugs. Fines for possession would increase for intoxicated drivers.

It appears probable but not certain that the legislation will be enacted by the House of Commons within the next few months. Prime Minister Jean Chrétien has publicly come out strongly for decriminalization, and so have the three candidates running to succeed him for the leadership of the governing Liberal Party.

Several backbench Liberal lawmakers have spoken out against the legislation, however, complaining that the legislation does not set tough minimum sentences for growers and traffickers and sends the wrong signal to youth.

"We're removing the stigma attached to the product and sanctioning or tolerating its use as produced by major elements of organized crime throughout Canada," the Liberal member of Parliament from Ontario, Dan McTeague, complained in an interview. "It is by no means a done deal as far the Parliament is concerned. This bill is going to have a difficult time."

Mr. McTeague noted that United States Customs has reported a "staggering" increase in seizures of Canadian marijuana crossing the American border. He said United States Customs seizures of 814 pounds of marijuana in 1998 increased to 2,650 pounds in 2001 and to 20,893 pounds last year.

The huge increase in 2002 is in part related to increased surveillance at the border in the wake of the Sept. 11, 2001, terrorist attacks.

Cultivating and trafficking marijuana are major businesses in Canada, run by biker gangs and Asian organized crime. Marijuana is estimated to be the third largest agricultural crop in both Ontario and British Columbia.

Pressure to reform the marijuana laws has been building for some time because of the drug's common use in several provinces, a string of lower court rulings and a constitutional challenge in the Supreme Court to legalize the drug. Recent polls show that most Canadians believe that youths caught possessing small amounts of marijuana should not be penalized with a lasting criminal record.