WASHINGTON -- Bringing home millions of dollars in special projects known as "earmarks" has long been a treasured practice on Capitol Hill -- one that can boost a member's stature in his district by suggesting prowess on the Hill.

But the questions Sen. Arlen Specter, R-Pa., faced this week, after the disclosure that $50 million in earmarks penned by his office went to companies that were clients of a lobbying firm headed by his aide's husband, were just the latest illustration of how those seemingly insignificant projects can create big appearance problems.

And it is also why some longtime opponents of earmarking, including Sen. John McCain, R-Ariz., have introduced legislation to curb the practice, and think it might actually have a chance of passing this year.

Mr. Specter does not believe his former appropriations aide, Vicki Siegel, played a role in inserting the special projects for her husband's clients into defense appropriations bills, because his office was able to provide the names of other people who lobbied for the projects. But the Pennsylvania senator also acknowledged that he wasn't familiar with many of the multimillion-dollar projects inserted into legislation at the behest of his office.

"We get -- I don't know how many hundreds of earmarks. ... On my subcommittee staff, we deal with thousands of them," Mr. Specter said this week. "I can't go over them all and evaluate them; that's why I have a staff."

But that sort of response-- and it is a common one from lawmakers -- exasperates people like Keith Ashdown, a vice president at Taxpayers for Common Sense, who sees the earmarking process as one of the secretive ways that Congress spends billions of dollars each year.

"Staff writes [the earmarks], and there's sort of a symbiosis there, because if some subterfuge occurs, [members of Congress] have a level of deniability," Mr. Ashdown said. Lawmakers, he said, "can deny the bad things and take credit for all the good things, and that's not just [Mr. Specter]; all of them do it."

Mr. Ashdown's group catalogued $24 billion in 6,371 earmarks in the highway spending bill last year. It is now wading through nearly 3,000 earmarks in the defense appropriations bill passed last year, which he expects to amount to more than $11 billion.

Taxpayers for Common Sense likes to remind people that, in 1987, then-President Ronald Reagan vetoed a highway bill because it contained more than 120 pet projects for lawmakers -- an amount that the president considered over the line. Mr. Ashdown estimates that House and Senate appropriations committees now receive more than 70,000 requests each year.

Mr. McCain recently cited a Congressional Research Service statistic that the number of earmarks in appropriations bills increased from 4,126 in 1994 to 15,877 last year.

The Arizona senator introduced legislation earlier this month that would try to create more transparency in the process. If a member found an unauthorized spending item, he or she could use a procedural move, known as a point of order, to force a vote on that specific provision, and it could be removed from the legislation without killing the whole bill.

Any special projects included in a final bill would have to be marked with the name of the member requesting the funding and an explanation of why the government should pay for the project. At present, unless a member publicly takes credit for a project, it is often difficult to tell who slipped it into a bill.

Mr. McCain's legislation would also ensure that members have 48 hours to review a major spending bill once it is finalized. That is intended to avoid the last-minute addition of earmarks that is so commonplace. Seven Republicans and two Democrats have signed on to the legislation, but Pennsylvania's two Republican senators, Mr. Specter and Sen. Rick Santorum, are not among them.