Boxer, D-Calif., and Bond, R-Mo., issued a statement saying 17 of their Senate colleagues signed a letter asking the Senate Appropriations Committee to find funding for the airlifter.
Those who signed include some of the most influential senators, including Dianne Feinstein, D-Calif.; Orrin Hatch, R-Utah; and Joseph Lieberman, I-Conn.
A similar letter-writing effort led by local Reps. Laura Richardson, D-Long Beach, and Dana Rohrabacher, R-Huntington Beach, is under way in the House of Representatives.
The issue pits members of Congress against President Barack Obama, whose administration last week released a budget recommending that the production line be shuttered. Defense Secretary Robert Gates has said the military has enough C-17s to meet its needs.
A Boxer spokeswoman in Washington, D.C., referred a press call to a statement issued by the senator.
"Congressional support for the C-17 program remains high because the aircraft has an impressive record of providing airlift support to our troops in combat zones and those working on humanitarian missions around the world,"` Boxer said, according to the statement.
At stake are more than 5,000 jobs in Long Beach, where officials said they remain optimistic that members of Congress from both parties will work to fund future orders.
"We continue monitoring the situation," said C-17 project spokesman Jerry Drelling. "We are very appreciative of the support we've received in the Senate."
Also on Tuesday, Boeing delivered its 187th C-17 to Charleston Air Force Base in South Carolina. Boeing is filling 205 USAF orders.
The Chicago-based aerospace giant recently received a U.S. Air Force contract valued at up to $400 million for two of the aircraft intended for use by NATO allies and Sweden and Finland. Before that, a House panel proposed adding $2.2 billion for eight C-17s to Obama's pending war request.
Boeing, which has five international orders in production, is aggressively seeking more from outside the United States.
However, Drelling said international orders alone cannot sustain the C-17 program because U.S. production keeps prices affordable.
"We need a healthy U.S. production line," Drelling said.
Existing orders should keep the cargo-plane line going through 2011.