PASADENA, Calif. — In a flawless, triumphant technological tour de force, a plutonium-powered rover the size of a small car was lowered at the end of 25-foot-long cables from a hovering rocket stage onto Mars early on Monday morning.

The rover, called Curiosity, ushers in a new era of exploration that could turn up evidence that the Red Planet once had the necessary ingredients for life — or might even still harbor life today. NASA and administration officials were also quick to point to the success to counter criticism that the space agency had turned into a creaky bureaucracy incapable of matching its past glory.

“If anybody has been harboring doubts about the status of U.S. leadership in space,” John P. Holdren, the president’s science adviser, said at a news conference following the landing, “well, there’s a one-ton, automobile-size piece of American ingenuity, and it’s sitting on the surface of Mars right now.”

Only one other country, the Soviet Union, has successfully landed anything on Mars, and that spacecraft, Mars 3 in 1971, fell silent shortly after landing.