A private venture hailed as the beginning of a new age of cheap and reliable access to space suffered a setback yesterday when its first rocket was lost over the Pacific Ocean about a minute after liftoff.

The rocket, called Falcon, was being launched from Omelek Island in the Marshall Islands by SpaceX, a company that has $200 million in contracts from the Pentagon, foreign governments and private companies to put small payloads in orbit. The company said Falcon was carrying an Air Force satellite.

The founder of SpaceX, Elon Musk, said in a statement, "We had a successful liftoff, and Falcon made it well clear of the launch pad, but unfortunately the vehicle was lost later in the first-stage burn."

In an interview, a spokeswoman for the company, Diane Molina, said no further information would be available until SpaceX had a better idea of what went wrong. Mr. Musk has put $100 million of his fortune from dot-com ventures like PayPal into the space company. He has been an evangelist for the notion that going to space, for cargo and human flight, could be far cheaper than the systems paid by governments and large contractors.