Marijuana is the most widely used illegal substance. About 15 million Americans smoke it, and police make nearly 700,000 pot-related arrests each year, accounting for nearly half of all drug arrests.

The $35 billion-a-year war on drugs has turned largely into a war on marijuana, and a losing war at that. Pot isn't harmless, but shouldn't law enforcement focus more of its resources on hard drugs — cocaine, heroin and methamphetamines — that are associated with violence and devastated lives?

According to a new study by The Sentencing Project, a liberal research group that favors alternatives to incarceration:

• Marijuana arrests increased 113% from 1990 through 2002, while arrests for all other drugs rose just 10%.

• Four of five marijuana arrests are for possession, not dealing.

The theory behind the war on drugs is that enough arrests will curtail both supply and demand. But the impact of increased marijuana arrests appears negligible. According to private and government studies, overall marijuana use is the same as it was in 1990, while daily use by high school seniors has nearly tripled, from 2.2% to 6%. Since 1992, the inflation-adjusted price of pot has fallen about 16% while potency has doubled, the studies show.

So the intensified crackdown has coincided with cheaper, stronger pot that's readily available. Law enforcement's efforts to arrest marijuana smokers are diverting resources from combating other crimes and those who traffic in hard drugs.

Few people arrested for possessing marijuana serve jail time, but the consequences they face are severe. They may not qualify for federal student loans or entry to public housing, may lose the right to vote, and face a job market with criminal records they must report to potential employers.

The drug war against low-level users also sparks resentment against police, particularly in the minority community. African-Americans represent 14% of marijuana users but account for 30% of arrests, The Sentencing Project study found.

The get-tough approach is showing cracks both at home and abroad. Twelve states have some form of decriminalization or reduced sentences. Great Britain, Canada and Russia have decriminalized possession of small amounts of the drug.

Today's more potent marijuana carries substantial health and social risks. It can lead to depression, thoughts of suicide and schizophrenia, especially among teens, according to government research. Its use should be discouraged. But it's a smoke screen to suggest that rising arrest numbers show the war on drugs is working. It's time for a serious debate on whether massive arrests of low-level users are worth the cost or having any benefit.