Clinton and Zedillo met at an opulent 17th century Yucatan hacienda as part of a 24-hour summit that also resulted in a flurry of accords on reducing violence along the two countries' border and providing $4 billion in credits to finance U.S. exports to Mexico.
The two announced an accord to liberalize border-crossing air transport as well as pacts to fight tuberculosis on both sides of the border.
The summit was overshadowed by U.S. debate on whether to add Mexico to a blacklist of countries not doing their part to stem the flow of illegal narcotics into the United States, an annual process viewed in Mexico as one-sided and hostile.
Monday's accord establishes so-called Bi-National Performance Measures of Effectiveness that will monitor both countries' progress in fighting narcotics demand, production and distribution, as well as combating drugs-related corruption and money laundering.
The accord provides "objective markers that the United States and Mexico can use to measure the success of our cooperative efforts to reduce the supply and demand of illegal drugs," a White House statement said.
"They also serve to identify those areas in which both nations can intensify their counter-drug activities," it added.
Clinton is expected to renew by March 1 an annual "certification" of Mexico as an ally in the drug war, despite opposition from several members of Congress who argue Mexico has lost ground in the anti-narcotics battle.
Decertification could mean a loss of some trade and economic benefits, but it would be a major embarrassment for both sides.
U.S. officials estimate that two-thirds of Colombian cocaine landing on U.S. streets crosses Mexican territory. Mexico is also a major producer of marijuana, opium and amphetamines. But Mexican officials note that U.S. demand for drugs fuels the trafficking.
Other law-enforcement agreements reached Monday would provide U.S. training to Mexican police and track chemicals used to make illegal drugs.
The presidential visit to Mexico comes as Hillary Clinton is seriously considering a run for the Senate in the year 2000, reports CBS News White House Correspondent Bill Plante.
Whether she does this or not sends a message that both she and the president have too much on their plate to look back.
Echoing that point, the Clintons visited the press cabin of Air Force One on Sunday night -- after months of avoiding reporters -- to pass out chocolates from a huge heart-shaped box.
"Happy Valentine's Day," the president said. "Isn't this the biggest heart you ever saw in your life?"
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