"I am 100 percent committed to the future of NASA," President Obama told the 200 people gathered at Kennedy Space Center in Florida, a statement intended to counter critics — including former astronauts — who have said his plans for the National Aeronautics and Space Administration would abandon the agency's heritage.

KENNEDY SPACE CENTER — President Obama, standing Thursday near a mock-up of the capsule he hopes will one day carry astronauts to deep space, rejected criticism his administration was scrapping America’s human-spaceflight program and outlined a program that would have astronauts flying to asteroids beyond the moon in a little more than a decade and circling Mars by the mid-2030s.

“I am 100 percent committed to the future of NASA,” he told the 200 people gathered at Kennedy Space Center in Florida, a statement intended to counter critics — including former astronauts — who have said his plans for the National Aeronautics and Space Administration would abandon the agency’s heritage.

The speech sets the stage for a showdown with critics in Congress who have opposed Obama’s plans to cancel NASA’s Constellation moon-rocket program and replace it with a “transformative” plan focused on developing new technologies Obama said would ensure America’s leadership in space for decades to come.

“The bottom line is that no one is more committed … to human spaceflight than I am,” the president told a group that included NASA Administrator Charlie Bolden, Florida politicians, aerospace-industry executives and Apollo astronaut Buzz Aldrin.

“But,” he said as applause swelled, “we’ve got to do it different.”

Obama’s speech was applauded by commercial rocket executives and even some congressional critics. U.S. Rep. Suzanne Kosmas, D-Fla., who flew with Obama aboard Air Force One, called his plan “steps in the right direction,” citing Obama’s decision to spend $1.9 billion to upgrade the space center and to put the center in charge of NASA’s commercial-rocket operation.

But Kosmas, along with U.S. Rep. Bill Posey, R-Fla., continued to call for an extension of the space shuttle to preserve some of the 9,000 space-center jobs that will be lost when the shuttle is retired, as planned, after three more launches. Obama, however, made no reference to extending the shuttle, which would cost more than $2 billion a year.

U.S. Rep. Rob Bishop, R-Utah, who represents the district where the first stage of Constellation’s Ares I rocket was being manufactured by rocket maker ATK, lashed out at the president. “President Kennedy opened the door to the new frontier, but Obama has slammed it shut and thrown away the key,” Bishop said.

In his speech, Obama laid out the reasons why he was canceling Constellation, which has cost $9 billion but is “behind schedule and over budget.” He said he would retain only the program’s Orion capsule.

Orion, he said, would form the basis for a new spacecraft that would fly on top of a new rocket capable of reaching deep space.

Obama said his budget would add $6 billion to NASA’s funding over five years, including extra money for satellites to monitor the Earth’s climate, a new space telescope, deep-space robotic probes and extending the life of the space station to 2020. He also said manned capsules will be circling Mars by the mid-2030s, with landing soon after.

“I expect to be around to see it,” he said.

Obama said his program would spend $1.9 billion over five years to modernize the aging spaceport and has given a federal agency task force an Aug. 15 deadline to set up a $40 million job-transition plan for space-center workers.

Obama would have NASA use commercial-rocket companies to resupply the international-space station with crew and cargo.

The rockets could include existing Delta IV and Atlas V rockets and new spacecraft being designed and built by SpaceX and Orbital Sciences.