WASHINGTON -- U.S. Sen. Dianne Feinstein is urging Mexican President Vicente Fox to personally look into his country's surging imports of pseudoephedrine, which drug cartels have used to make tons of methamphetamine for U.S. consumption.

In a letter to Fox sent Thursday, the California Democrat cited a June 5 report in The Oregonian that revealed Mexico's imports had shot from 66 tons in 2000 to 224 tons in 2004 -- almost twice the amount needed to meet legitimate demand for cold medicine.

The newspaper's analysis concluded that much of the surplus was going to meth "superlabs" south of the U.S. border.

Feinstein, calling The Oregonian's findings "credible, and deeply concerning," told Fox that his country was importing "inordinate amounts of pseudoephedrine" and that those imports were fueling the meth trade.

The situation "indicates the growing transnational reach of the methamphetamine problem," Feinstein wrote. "It also calls for international efforts.

"To that end, I strongly urge you to personally examine this issue. I am confident that with your leadership, Mexico can take effective steps to limit, and maybe even eliminate, the flow of this horrible drug through your country."

Copies of the letter went to Secretary of State Condoleezza Rice and Attorney General Alberto Gonzales.

Although not an official diplomatic communique, a letter from a U.S. senator from a large border state can carry weight with the government of Mexico.

"It's not a slam dunk to change policy, but I certainly think it can matter," said Nancy E. Roman, vice president and director of the Council on Foreign Relations, Washington Program.

A spokesman for the Mexican Embassy in Washington, D.C., said the government had no immediate response to Feinstein's letter. However, the embassy released a list of actions that Mexican authorities have taken to deal with methamphetamine and pseudoephedrine in recent years titled, "Mexico's Fight Against Methamphetamines."

The actions included designating special federal prosecutors to handle cases in which pseudoephedrine is diverted to the meth trade, confining the sale of pseudoephedrine products to pharmacies, and communication between the two governments on drug-related chemicals "on a daily basis."

Tons of vanishing pills

Mexican pharmaceutical companies import pseudoephedrine mainly from India, China and Germany for the production of cold medicine.

Although importers, manufacturers and wholesalers are regulated by the government, the finished pills have disappeared in large quantities all along the distribution chain.

Mexican officials have said they are aware of the sharp increase in imports and have moved to roll back imports by 30 percent this year.

But The Oregonian's analysis showed that this reduction would still leave a surplus of 28 to 65 tons available for diversion to the meth trade. Through April, the country had imported 69 tons, which would put it on a pace to import almost as much in 2005 as it did last year.

Mexico is now the leading source of meth sold in the United States, according to the U.S. Drug Enforcement Administration.

The agency estimates that 65 percent of meth sold in the United States is now manufactured by Mexican drug trafficking organizations: 12 percent in their U.S.-based superlabs and 53 percent in Mexico.

The remaining 35 percent is made by small home labs operated by U.S. meth users, according to the DEA.

U.S. officials believe that Mexican superlab production is on the rise. Meth found crossing the U.S. border with Mexico nearly doubled from 2002 to 2004, according to DEA officials.

The Oregonian reported in October that large-scale meth production by Mexican traffickers is uniquely vulnerable to disruption, because superlabs rely on vast quantities of legal chemicals that originate in a limited number of factories worldwide.

Past efforts to clamp down on the flow of ephedrine and pseudoephedrine to the superlabs have caused meth prices to soar and users to quit. But the pressure was not maintained because of loopholes in federal law, inconsistent enforcement, and eventually the availability of the chemicals in other countries.

No system exists to ensure that countries import no more pseudoephedrine than they need.

Last week, a group of about 20 U.S. House members began discussing legislation or diplomatic measures to track the pseudoephedrine trade internationally. But Feinstein's letter is the highest-profile public pronouncement on Mexico's pseudoephedrine imports so far.

Feinstein, with Sen. Jim Talent, R-Mo., is sponsoring legislation this year that would place pseudoephedrine behind the pharmacy counter, as Oregon and other states have done. If that succeeds in cutting production by small-time labs in the United States, some law enforcement officials fear Mexican-made meth will replace the local supply.

Rep. Ken Calvert, R-Calif., co-chair of the congressional meth caucus, said he supports Feinstein's move. Dealing with local meth labs is important, he said, "but we also have to run a two-front operation."

If a company in Mexico imports more pseudoephedrine than necessary, he said, "we ought to be able to put pressure on that company to stop, or there will be some consequences to it."