President Bush promoted free trade and democratic values Friday at the opening of 34-nation summit meeting in Argentina, but his trip got off to a rough start when tens of thousands of demonstrators turned out to protest and violent splinter groups clashed with Argentine police.

As leaders of the Western Hemisphere were meeting in this seaside resort, site of the Summit of the Americas, about 40,000 protesters gathered in a Mar del Plata stadium for a rally against Bush and globalism. Bush's leading critic in South America, leftist Venezuelan President Hugo Chavez, told the crowd he had come to bury the Free Trade Area of the Americas (FTAA), a stalled trade pact that Bush has sought to advance.

"Every one of us has brought a shovel, an undertaker's shovel, because here in Mar del Plata is the tomb of FTAA," Chavez declared, Reuters news agency reported. With Chavez was former Argentine soccer star Diego Maradona, who carried a Cuban flag and wore an anti-Bush T-shirt.

After the rally, the generally festive protesters split into various demonstrations, and small gangs of violent young men rampaged through the streets, vandalizing businesses and clashing with some of the 7,500 police guarding the summit site. The violent demonstrators broke shop windows, set fire to an Argentine bank branch with gasoline bombs and hurled rocks at police in riot gear. Police responded by firing tear gas.

Groups of 10 to 20 young men, most of them wearing bandanas over their faces, attacked a number of businesses and set street fires with furniture they looted from them. Outside an American satellite television service, one of the roving bands had pulled cabinets into the street and set them ablaze.

Earlier, thousands of demonstrators had marched in the streets of Mar del Plata to protest the U.S. president's visit, shouting such slogans as "Get out Bush!"

For Bush, the trip was aimed in part at improving America's tarnished image in Latin America. But in addition to the protests, he was dogged by his political troubles at home.

In a brief news conference with U.S. reporters accompanying him, Bush skirted questions on the fate of top strategist Karl Rove, possible White House staff changes and his plummeting job approval ratings.

Sticking to a position he has adopted in recent weeks, Bush said he would not discuss Rove, the White House deputy chief of staff, until an investigation of his role in a CIA leak case is complete. Nor would he say anything about calls for a staff shakeup in the White House in the wake of last week's indictment of Vice President Cheney's chief of staff, I. Lewis "Scooter" Libby, on charges of lying to FBI agents and a federal grand jury about the leak to reporters of CIA agent Valerie Plame's identity. Libby resigned and left the White House when the indictment was returned. He pleaded not guilty Thursday.

Asked if he owed the American people an apology for his administration's past assertions that Rove and Libby were not involved in the leak, Bush said, "I'm not going to discuss the investigation until it's completed."

He added: "My obligation is to set an agenda, and I've done that. And the agenda's fighting and winning the war on terror and keeping the economic vitality and growth alive, dealing with the energy problem, nominating people to the Supreme Court that adhere to the philosophy that I campaigned on."

Bush brought up his nomination of federal appeals court Judge Samuel A. Alito Jr. to the Supreme Court, expressing disappointment that the Senate Judiciary Committee will not begin confirmation hearings before Christmas, as he had requested. The committee chairman, Sen. Arlen Specter (R-Pa.), has set the start of the hearings for Jan. 9.

"I'm disappointed in the date, but happy they do have a firm date for his confirmation hearing," Bush said. He raised the issue again later in the 15-minute news conference as he sidestepped a question on his poll ratings, saying the nomination was "a very vital issue" for the Senate and for the nation and calling Alito "an incredibly intelligent, well-qualified person who should be on the court." He said Specter told him hearings could not be held before Christmas because Alito "had written so many opinions, and he wanted to make sure he had time to read them."

Asked about polls that indicate a majority of Americans question Bush's honesty and put his approval rating at an all-time low -- 39 percent in a Washington Post-ABC News poll published today -- Bush stammered that he has been asked about polls repeatedly in the past. Then he said: "The way you earn credibility with the American people is to set a clear agenda that everybody can understand, an agenda that relates to their lives, and get the job done. And the agenda that I'm working on now is one that is important to the American people."

Regarding a prospective encounter with Chavez, his most outspoken critic at the summit, Bush said, "Well, I will, of course, be polite. That's what the American people expect their president to do is to be a -- you know, a polite person."

Bush said he judges foreign leaders based on their willingness to protect democratic institutions and vowed that the United States "will speak out" when leaders violate basic freedoms. But he said his government can do so by "not necessarily singling out a particular country or person, but talking on the positive" and stressing the importance of democratic values.

"I think this is a good forum and a good opportunity . . . for me to express our country's values," Bush said. "But they're not American values. I keep telling you these are universal values . . . that are true."

Bush said he had also discussed economic progress, regional free trade agreements and the investment climate in meetings with the president of Argentina, Nestor Kirchner, and with the leaders of Central American and Andean nations.

After his meeting with Kirchner, Bush thanked the Argentine president, saying, "It's not easy to host all these countries. It's particularly not easy to host, perhaps, me."

Kirchner, a populist who has had cool relations with Bush, said he was "very satisfied" with his "candid" talks with Bush, "because it wasn't a meeting looking for nice words, but to speak the truth, and each of us did just that."

Branigin reported from Washington, D.C.