COLUMBUS, Ohio - It's one of Republican presidential candidate John McCain's most surefire applause lines, a vow to veto pork barrel spending like the road and bridge projects that lawmakers hold dear.

"You will know their names. I will make them famous," he tells his appreciative audiences.

Yet three times in recent weeks, the Republican presidential candidate supported legislation allowing thousands of these and other projects to go forward at a cost of billions of dollars. It's an awkward acknowledgment of the difficulty McCain - or any chief executive - faces in stamping out lawmakers' pet projects.

"The reality is that the Constitution invests the Congress with a great deal of power with respect to spending," said Scott Lilly, a Democrat and former top staff aide on the House Appropriations Committee.

"Presidents almost always have programs that they want to implement that they need the cooperation of Congress to get," Lilly said. "Presidents are generally quite willing to do that because they cover a fraction of a percent of total discretionary spending and an even smaller fraction of the overall budget."

Rob Portman, a former Ohio congressman and budget director under President Bush, said, "The trend is in the right direction," with the number of so-called earmarks declining in recent years. Portman, a strong supporter of McCain, added in an interview that the only sure solution would be to give the president authority to reject individual parts of the massive spending measures that Congress typically passes.

Routine spending bills often combine dozens if not hundreds of such projects, and lawmakers who are eager to protect their own are loath to vote against someone else's.

Congressional rules often prohibit votes on individual issues.

And leaders in both parties and both houses of Congress frequently combine several measures into one, calculating that the overall package will be politically difficult if not impossible to oppose.

That was the case late last month with legislation whose original purpose was to keep the government running after the Oct. 1 start of the fiscal year.

By one count, the measure included 2,322 pet projects sought by lawmakers for their home districts and states, at a cost of $6.6 billion. It also included billions of dollars in federal loan guarantees for the auto industry, and allowed a moratorium on offshore oil drilling to expire.