President Bush arrived in this seaside resort Thursday night for a summit with other leaders from the Western Hemisphere, during which he hopes to promote lower trade barriers as a tonic for poverty and joblessness throughout the region.

The fourth Summit of the Americas was to open Friday under tight security. Thousands of police officers were stationed behind barricades that cordoned off large sections of this city, as officials sought to prevent the two-day meeting from being overwhelmed by demonstrations.

The Bush administration had hoped the meeting would help revive stalled plans for a Free Trade Area of the Americas, a zone that would stretch from Alaska to Argentina.

"From our point of view, the Free Trade Area of the Americas has defined the summit process," said Thomas A. Shannon Jr., assistant secretary of state for the Western Hemisphere.

But that message was at odds with the sentiment in much of Latin America, where millions of people have yet to realize the promised benefits of democracy and free trade.

Across the region, half a dozen populist leaders have been elected in recent years, often supported by constituencies that blame U.S.-backed economic policies, private investment and international trade as sources of continued poverty and widening income disparities.

"What we're looking to do is find ways to unlock some of these economies so they get the kind of investment they need, they get the kind of trade they need and they have the flexibility within their labor markets to generate employment," Shannon said.

Venezuelan President Hugo Chavez, who for years has swapped harsh rhetoric with the Bush administration, has described the proposed free trade zone as an "imperialist plan" to enhance U.S. economic dominance over Latin America and the Caribbean.

In its place, Chavez is calling for greater integration of South American economies, a vision he has pursued by offering oil from his nation's vast reserves to Venezuela's neighbors at reduced rates.

Chavez has said he wants to debate the U.S. economic approach during the summit. He plans to address a rally Friday denouncing the free trade plan.

Bush is scheduled to visit Brazil and Panama after the summit, then return to Washington Monday night.

President Bush upon landing in Argentina for the two-day meeting.