Though Defense Secretary Robert Gates has recommended discontinuing funding for the Long Beach-built military cargo plane, Boxer and Bond said a joint news release that they want to put the C-17 in the Fiscal Year 2009 Supplemental Defense Appropriations Bill.
The senators are circulating a letter to their colleagues calling on the Senate Appropriations Committee to include funding in the bill to procure 15 additional airplanes.
A final, signed letter will be sent to the Appropriations Committee, Boxer spokeswoman Natalie Ravitz said in an e-mail sent from the Senate floor.
Failing that, Boxer will consider her options on the Senate floor, Ravitz said, adding "right now, we are focused on working with the Appropriations Committee on this matter."
Boxer also issued a statement:
"The C-17 has an impressive record of providing airlift support to our troops serving in combat zones and those working on humanitarian missions at home and around the world.
"Given the kind of missions we anticipate in the future, it would be foolhardy to shutter this line when we are unsure of our future airlift needs and we are making strides in developing an overseas market for these aircraft."
In the letter, Bond and Boxer say that the C-17 has been an "indispensable asset" since it began service in 1993.
Reps. Laura Richardson, D-Long Beach, and Dana Rohrabacher, R-Huntington Beach, have gone to bat - they made appropriations requests and are lobbying their peers - for the cargo plane in the House of Representatives.
A Boeing spokesman affiliated with the C-17 could not be reached Thursday, but the company has said in the past that it supports the politicians' efforts.
At stake are some 5,000 jobs at the Long Beach Boeing plant and a network of 30,000 supplier jobs nationwide.
Some feared that the C-17 line would close this year, but the line will continue until at least August 2010, thanks to a $2.95 billion Air Force contract to build 15 more planes.
Though Gates and the Pentagon make recommendations on the military budget, Congress controls the purse strings.
Where President Obama stands on the C-17 is unclear. Obama expressed strong support for the plane earlier this year, but Gates, a cabinet member, has said the country must plan for a different type of combat future that doesn't necessarily require additional C-17 purchases.