The commercial rockets would displace the Ares I, the rocket that NASA has been developing for the past four years to replace the shuttles, which are scheduled to be retired this year. Companies expected to seek the new space taxi business include United Launch Alliance, a partnership between Boeing and Lockheed Martin that launches rockets for the United States Air Force, and Space Exploration Technologies, a start-up company led by Elon Musk, who founded PayPal.

Speaking at a news conference in Israel on Wednesday, Gen. Charles F. Bolden Jr., the NASA administrator, gave hints of the new direction. “What NASA will focus on is facilitating the success of — I like to use the term ‘entrepreneurial interests,’ ” General Bolden said.

Skeptics wonder whether the commercial approach would be significantly faster or cheaper than completing the Ares I and the Orion capsule that would carry the astronauts, and how astronaut safety would be maintained. NASA has spent about $9 billion on Ares I and Orion.

“We have already spent valuable time and billions of dollars developing this program,” Representative Michael McCaul, Republican of Texas, said in an e-mail statement. “It makes no sense to throw away a plan backed by 50 years of NASA experience and institutional knowledge in favor of start-up operations, which may encounter delays and unknown obstacles.”

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Mr. Obama’s proposal would further dismantle what remains of the human spaceflight initiative started by the Bush administration in 2004. Last year, $3.5 billion in spending was cut from President George W. Bush’s NASA budget projection for 2011 through 2013, money that would have been used to develop the lander that was to return astronauts to the moon by 2020.

The proposed budget increase would also be much less than the $3-billion-a-year increase that a blue-ribbon committee appointed by the Obama administration said was needed for NASA to successfully pursue a human spaceflight program beyond low-Earth orbit.

As widely expected, Mr. Obama’s request will seek to extend the life of the space station five years, to 2020. It also proposes investments to improve the facilities at the Kennedy Space Center.

The retirement of the space shuttles will cost at least 4,600 of the 15,000 jobs at the Kennedy Space Center. The administration official said the commercial launching initiative could create up to 1,700 jobs in Florida, but that figure is based on projections of the Commercial Spaceflight Federation, a trade group.

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Sally K. Ride, a former astronaut who served on the blue-ribbon panel, said she was encouraged by the budget increase for NASA in light of the planned freeze on domestic spending over all.

“They plan to be sending people beyond low-Earth orbit, and they have a good formulation,” Dr. Ride said. “I think the way to evaluate this plan when it’s rolled out is to ask whether the administration has given NASA the funds for what it’s asked to do.”

“It appears to me the answer is yes,” Dr. Ride said, based on briefings she had received on the plans.

She said the administration took options the panel presented and “came up with an innovative approach for NASA.”