Over the objections of the Air Force, Sen. Christopher S. Bond (R-Mo.) used closed-door congressional negotiations, which ended last week, to win a guarantee that the Boeing Co. plant in St. Louis will keep producing F-15 fighter-bombers at least through the end of 2008.

The maneuver shed light on the grass-roots politics swirling around the writing of the 2005 defense spending bill, a sprawling $416 billion measure stuffed with hundreds of projects earmarked by lawmakers but not sought by the Pentagon. House and Senate conferees agreed on a final version of the bill last week, and it was then quickly approved by Congress. It is now awaiting President Bush's signature.

For Bond, who is running for a fourth Senate term this year, extending the life of the F-15 assembly line -- set to run out of work in mid-2008 -- has been a top priority all year. Although recent polls show Bond running ahead of his main Democratic challenger, State Treasurer Nancy Farmer, some Democrats believe the race will tighten after their primary. Farmer, a rising Democratic star, was showcased as a speaker at the Democratic National Convention on Tuesday night.

Bond's news releases have cited strong labor union support for his F-15 initiative to ensure that jobs stay in Missouri. Senate Appropriations Committee Chairman Ted Stevens (R-Alaska), a friend and political ally, backed Bond's proposal to add $120 million for the F-15 program.

But according to congressional aides in both parties, senior Air Force officials are concerned that prolonging F-15 production could weaken support in Congress for Lockheed Martin Corp.'s newer but costlier F-22 fighter, a top Air Force priority that is now in its test phase at Edwards Air Force Base in California.

The F-22 was initially intended as a replacement for the F-15, with a primary mission of defeating enemy planes in aerial combat. However, an updated F-15 version, the Eagle, became a workhorse in conflicts in the Persian Gulf theater, delivering "smart" bombs to targets in Iraq and Afghanistan and gathering intelligence, as well.

That record has led some mid-level Air Force officers, and some lawmakers, to raise the possibility of reducing purchases of the F-22 while continuing to outfit some squadrons with new, upgraded F-15s.

Speaking on the Senate floor last week, Sen. John McCain (R-Ariz.), a senior member of the Senate Armed Services Committee, listed the added $120 million for the F-15 in a $8.9 billion "pork" list of projects included in the defense spending bill even though they were not sought by the military services. On the list were hundreds of projects, including $1 million for the biathlon trail at Ford Richardson, Alaska; and $1.9 million for the Lewis and Clark bicentennial celebration.

Noting that the F-22 was supposed to be a replacement for the F-15, McCain said the decision to extend production forced him "to question the necessity of the F-22 procurement in the numbers of aircraft and at the funding levels requested by the Air Force. Apparently, we just decided to pay for both."

In 1997, Congress, concerned about the long-range cost of the F-22 program, set a ceiling of $36.8 billion for the life of the program. That top number has forced the Air Force to reduce its goals for numbers of planes as the costs of the aircraft have risen to about $150 million each, nearly twice that of the F-15.

Bond initially had the additional F-15 funding placed in the Senate version of the 2005 defense spending bill, but it was not in the House-passed bill. And neither the House or Senate versions of the pending 2005 defense authorization -- which sets policy for the military -- included the funding.

"Senator Bond is highly regarded by me," said Sen. John W. Warner (R-Va.), who chairs the Senate Armed Services Committee, which writes the separate authorization bill. But he said that he had had no contact about the issue with Bond, a senior member of the Senate Appropriations Committee, which produces the defense spending measure.

"There is a world of difference between the 15 and the 22," Warner said. "This country must step forward with the F-22."

The behind-the-scenes battle is indicative of the political stakes -- and the grass-roots impact -- of almost every line in the defense bill.

Boeing's Seattle plant supplies avionics and parts for the F-22, but the plane is mainly built in the Fort Worth and Marietta, Ga., plants of the prime contractor, Lockheed Martin. While Bond was on the House-Senate team that negotiated the final defense bill, Georgia was not represented. Texas's sole negotiator, Sen. Kay Bailey Hutchison (R), is junior to Bond on the Senate Appropriations Committee.

Yesterday, Boeing spokesman Doug Kennett said the company "appreciates Senator Bond's strong leadership on the F-15 issue."

Researcher Madonna Lebling contributed to this article.

The new F-22 fighter, left, made by Lockheed Martin Corp. at $150 million apiece, was set to replace the older F-15, produced by Boeing Co. But upgraded F-15s, at about half the cost, have been versatile workhorses in recent combat, leading some officers and lawmakers to question the need for the new plane. Sen. Christopher S. Bond got $120 million earmarked for building new F-15 fighters.