BARILOCHE, Argentina - Secrecy surrounding a military agreement between the U.S. and Colombia has critics warning of a new Yankee menace to the continent. Leaders at Friday's South American summit want assurances they won't be targeted.

U.S. and Colombian diplomats have spent weeks trying to calm fears since The Associated Press reported details of the agreement to give the U.S. military a 10-year lease on space at seven Colombian bases to help fight drug traffickers and leftist rebels.

The deal is done -- just awaiting signatures, according to Colombia's foreign minister -- and Uribe has no intentions of backing down at the UNASUR summit of South American presidents.

The U.S. military has already operated in Colombia for years as part of Plan Colombia, $6 billion in U.S. aid that helped President Alvaro Uribe bring security to the violent nation.

But many regional leaders are worried the U.S. has other goals in mind.

A U.S. military document described one of the Colombian bases, Palanquero, as a potential jumping off point for U.S. forces, noting that "nearly half the continent can be covered by a C-17 (military transport) without refueling."

U.S. officials have publicly stressed since then that the U.S. military will remain inside Colombia and only cross borders when invited by other countries.

But the explanation hasn't satisfied presidents Hugo Chavez of Venezuela and Rafael Correa of Ecuador, and other leaders remain uneasy. Brazil hopes to see Uribe make written guarantees at the summit, while encouraging others to tone down their rhetoric.

"I'm going to the UNASUR meeting to discuss peace for our beloved South America, which is feeling very nervous. We must find the path to peace," Brazilian President Luiz Inacio Lula da Silva said before heading to Argentina.

Chavez -- who has repeatedly denied accusations that he supports Colombia's leftist rebels -- said the deal loosed "winds of war." He warned that U.S. troops could use the bases to launch operations to unseat Latin American leaders like himself. He told his diplomats to prepare to break off relations with Colombia and talked of buying more Russian tanks.

"You can establish 70,000 Yankee bases surrounding Venezuela, but you aren't going to beat the Bolivarian Revolution!" Chavez declared this week.

Latin American leaders tend to be suspicious of foreign militaries in a region where only decades ago U.S.-backed dictatorships killed and tortured their own citizens. Chilean President Michele Bachelet is among the survivors.

The unresolved coup in Honduras -- by a military with close U.S. ties and training -- worries them as well.

And political instability provides a pretext for spending big on defense.

Even before news leaked about the bases deal, Venezuela poured about $4 billion into Russian weapons to counter the threat Chavez sees from U.S. military aid to Colombia.

Ecuador is buying 24 Brazilian warplanes and six Israeli drones to keep a closer watch on its borders. Bolivia has opened a $100 million line of credit with Russia to buy weapons.

Citing a need for modernization, the 12 UNASUR nations spent about $51 billion last year on their militaries -- up 30 percent from 2007, according to the Center for a New Majority, a Buenos Aires research group.

That's low compared to the rest of the world -- U.S. spending alone is well into the hundreds of billions -- but a steep burden for democracies in a relatively peaceful region struggling with poverty and economic crisis.

"None of this is good. The last thing the region needs is an arms race," said Markus Schultze-Kraft, a Bogota-based analyst with the International Crisis Group, a conflict-resolution organization.

Colombian Foreign Minister Jaime Bermudez said Uribe is prepared to make reassurances, but also may question his fellow presidents about their own military contracts.

Correa is hoping for more, saying Uribe's claim that the bases deal is an internal matter doesn't make sense. After all, Uribe already sent his military into Ecuadorean territory last year to kill a top rebel commander -- and said he would do it again.

"What if later we put nuclear warheads in Ecuador, and declare them to be a matter of national sovereignty?" Correa told Peru's Radioprogramas while traveling to the summit. "It's absurd -- these are things that endanger the whole region."

The presidents were greeted by a military band at the Andean ski resort. Chavez smiled broadly over his bright red scarf and Bolivia's Evo Morales dressed down in his trademark sweater, arriving just before the meeting hosted by Argentina's Cristina Fernandez.