An amendment to the defense authorization bill, sponsored by Sens. Jim Talent, R-Mo., and Joe Lieberman, D-Conn., would authorize the Air Force to purchase up to 42 new C-17s and create a new structure for the Defense Department to assess the need to build more lift aircraft.

The C-17 program appeared to be in jeopardy after a recent draft of the Defense Department's Mobility Capabilities Study recommended purchasing no C-17s beyond the 180 currently planned. With the last of the C-17s scheduled for delivery in 2008, production would start to wind down as soon as next year.

"The C-17 is the finest military transport in the world," said Talent, a member of the Senate Armed Services Committee. "This amendment is crucial to ensure that the United States has the airlift we need to deploy and sustain our forces overseas."

Most of the C-17 is built in California, but several components are assembled at Boeing's St. Louis-based defense unit. About half the Missouri jobs affected are in the St. Louis area, with the other portion divided among dozens of suppliers in the state.

Production of the C-17 generates $776 million in economic activity in Missouri.

Struggling to pay for a costly war in Iraq, the Pentagon is considering up to $15 billion in cuts to aircraft, shipbuilding and other weapons purchases as it begins to write a budget for next year.

The C-17 is the primary aircraft used to carry troops to the battlefield. The planes are used to haul some of the military's heaviest equipment and have been deployed for special operations missions, training and humanitarian relief missions, including responses to the Gulf Coast hurricanes.

"We sincerely appreciate the leadership of Sens. Talent and Lieberman on this critical issue, and the strong bipartisan support it received from the U.S. Senate," said Boeing spokesman Doug Kennett.

Loren Thompson, a defense analyst at the Lexington Institute think tank in Arlington, Va., called the C-17 a workhorse that has been valuable for the military.

"Without additional C-17s, it will be very hard for the Air Force to meet its obligations to the rest of the nation's military," Thompson said. "The Air Force doesn't want to stop production because it isn't very happy with its existing aircraft and it thinks it will need more C-17s, but it can't afford to keep producing them."

But the government watchdog group Project On Government Oversight called the amendment pork.

"This is just another gift to a defense contractor, the latest attempt by Congress to force the military to purchase weapons it doesn't even need," said Eric Miller, the group's senior defense investigator. "Congress is looking out for the defense industry but not the needs of our military."

The Senate is expected to approve the defense authorization bill this week. The bill will then go to a conference committee with the House, where lawmakers will press to include the C-17 measure.