U.S. AND MEXICO COORDINATE EFFORTS FOR MUTUAL PROTECTION

CIUDAD JUAREZ, Mexico, March 21 - The United States and Mexico, after
battling over their common border for so many years, are now coordinating
military missions to protect it from attack.

Mexico is sending thousands of soldiers to patrol the border and help
secure it against terrorist threats - an unprecedented move. The Mexicans
have never used their army to help defend their neighbor.

"It's a new mission: Mexico looking out for the United States," said Sgt.
Benito Hernandez, a Mexican soldier on sentry duty here in Juarez, where
thousands of travelers and truckers cross the border in both directions
every day.

Mexico is sending 18,000 soldiers to secure airports, seaports, border
posts and bridges with direct links to the United States. At least half
will be based within a few miles of the border, many serving as sentries in
the desert. Others will serve in the interior, guarding tourist resorts and
oil refineries, the two great sources of foreign revenue for Mexico.

The United States, for its part, has Special Forces, Army Rangers and
Marines to monitor thousands of square miles at the Mexican border with
night patrols, electronic sensors, pilotless drone aircraft first used 18
months ago in Afghanistan and helicopters with infrared scopes.

They are training their sights away from smugglers of drugs and migrants
toward the terrorist threat, erasing the "thin line between counterdrug and
counterterror missions" to quote Gen. John Yingling, one of their
commanders. The American military is moving closer to using its soldiers as
law enforcers, as Mexico has done for years.

Soldiers attached to General Yingling's Joint Task Force Six, based just
north of Juarez at Fort Bliss, Tex., have orders to support United States
drug enforcement. They "could also be effectively employed in the combating
terrorism effort," said their spokesman, Armando Carrasco. "Terrorism and
drug trafficking are intertwined and use many of the same operational methods."

They are under the new Northern Command headquarters in Colorado, which has
been given responsibility for overseeing the United States, Mexico and
Canada. The Northern Command includes officers of the C.I.A. and the
F.B.I., which in turn are sharing border security information with their
Mexican counterparts. The Federal Protective Police, Mexico's equivalent of
the F.B.I., is heavily involved in the new security mobilization, as is
Cisen, Mexico's equivalent of the C.I.A.

These linkages and the coast-to-coast mobilization by both nations
represents the birth of a international national-security network, American
and Mexican officials said.

"Mexico is not going to be used as a transit point for any terrorist or
anyone who wishes to harm the United States," said Interior Minister
Santiago Creel, who oversees Cisen. Mexico said hours after combat began in
Iraq that it would deny visas to travelers from a list of Arabic and Asian
countries deemed hostile to the war effort.

By collaborating against a foreign threat, both nations are crossing a line
that they had never breached.

"Despite the inherent distrust between both countries' law enforcement and
their militaries, they had to find a way to talk to each other and share
information," said Ana Maria Salazar, a former Pentagon official and an
expert in Mexican national security doctrine. "They were forced to figure
out a way to coordinate."

Mexico is striving to show political and military support for the United
States after rejecting President Bush's demand for its vote at the United
Nations Security Council for a war against Iraq.

Mexican officials are worried that the United States will extract a price
for that rejection by closing off the border, which would severely damage
Mexico's economy, or expel thousands of undocumented Mexican migrants in
the United States.

"You have to give the Americans a sense of security," Ms. Salazar said, "or
they will close down the border the moment they get an inkling of some threat."

Mr. Creel said Mexico felt "compelled to collaborate with the United States
to identify any potential risk" at the border "both against American
citizens or assets or here in our own country."

Here in Juarez, where four busy border crossings remain open, travelers and
truckers are being subjected to a higher level of scrutiny on the American
side of the border under the newly re-established Code Orange alert. The
level of cross-border trade between Mexico and the United States - more
than $250 billion a year - has not changed.

What has changed is the greater intensity of the flow of information
between the American and Mexican military and intelligence services,
officials said.

"It is impossible, really, to oversee the border, unless they put the
entire United States Army there," said Rafael Fernandez de Castro, a
foreign policy analyst in Mexico City.

"But the mobilization of 18,000 Mexican soldiers is a very big deal," he
said. "And the strategic coordination between the Americans and the
Mexicans has never been greater."