WASHINGTON -- Election year troubles often produce peculiar alliances and the most intriguing new partnership is that of Sens. John McCain and Rick Santorum on proposed changes to lobbying regulations.

At the Senate's first hearing on the issue this past week, Mr. Santorum sat dead center on the panel of senators, pledging to lead the charge for change while trying to persuade his colleagues and the public that it's a task for which he is suited.

But Mr. Santorum placed particular emphasis on his eagerness to work with Mr. McCain, who is described as the Senate's "reformer" so often that it has become cliche.

Mr. McCain's presence at Mr. Santorum's side as the Senate turns its attention to the lobbying overhaul is viewed as a major boost for the Pennsylvania senator as he tries to untangle himself from the controversy over the "K Street Project" -- a GOP effort to pump up the party's power and fill its coffers by getting more Republicans hired at Washington's lobbying firms.

Some of Mr. Santorum's supporters compare McCain's long struggle to tighten campaign finance laws and his investigation into the illegal activities of former lobbyist Jack Abramoff on the Indian Affairs Committee to Mr. Santorum's efforts more than a decade ago to shed light on the activities of House members who were bouncing thousands of checks at the House bank and trading postage stamps for cash.

"It's a natural alliance," said former Pennsylvania Republican state chairman Alan Novak. "Senator McCain is popular among independent voters and he's seen as principled leader in the Senate. ...But this issue reminds people that Santorum came to congress as a passionate reformer. ...It allows voters to once again view Senator Santorum in that way."

Ross K. Baker, a political science professor at Rutgers University who studies Congress, had a different take on Mr. Santorum's interest in working with Mr. McCain now.

"It's called political cover," Mr. Baker said, adding that Mr. Santorum has been the Republican leadership's liaison to the lobbying community through his weekly meetings with top Republican lobbyists.

Clearly there are benefits to Mr. McCain as well. If the Arizona Republican decides to run for president in 2008, Mr. Santorum's credibility with social conservatives could be critical in an area where Mr. McCain is weakest. And in the near term, Mr. Santorum's No. 3 role in the Senate leadership could ensure strong support for a package of proposed changes in lobbying rules. Mr. McCain's first attempt drew little notice when he introduced it in December before Mr. Abramoff pleaded guilty to fraud, tax evasion and conspiracy to bribe public officials.

But if the past is any guide, Mr. Santorum and Mr. McCain are likely to face major policy disagreements over the issues they are considering in the lobbying bill.

One only needs to look back several years to the debate over campaign finance reform.

Both Mr. McCain and Mr. Santorum have said this year's effort to alter lobbying rules should also address the influence of groups known as 527 organizations, tax-exempt political advocacy organizations that have poured money into political campaigns with few requirements to disclose who their donors are.

But Mr. Santorum was a chief opponent of Mr. McCain and Sen. Russ Feingold, D-Wisc., when they spent years in the Senate trying to pass a ban on "soft money" -- unlimited contributions to political parties -- and other changes to campaign finance regulations.

Mr. Santorum urged Sen. Mitch McConnell, R-Kentucky, to challenge the constitutionality of the law in court and told reporters he would "lay my body down in front of that train." In a letter to editor in the Post-Gazette in 2002, before the McCain-Feingold law had been upheld by the Supreme Court, Mr. Santorum explained his opposition to Mr. McCain's bill by saying he "would not stand by while members of Congress attempt to limit an individual's First Amendment right to free speech under the guise of a ban on soft money."

Another area where the two lawmakers are likely to disagree is on Mr. McCain's contention that Congress should end the practice of allowing lawmakers to tuck their special projects into major spending bills, which is often an anonymous act at the behest of lobbyists.

Mr. McCain and a handful of like-minded senators have fought against the practice by forcing lawmakers to publicly debate the projects, which are known on Capitol Hill as "earmarks."

The practice has gained notoriety lately after it was revealed that former U.S. Rep. Randy "Duke" Cunningham, R-Calif., used earmarks to pay off the defense companies that bribed him with money and lavish gifts.

But Mr. Santorum, like House Democrat Rep. John P. Murtha of Johnstown and others, has proved particularly adept at getting special projects through for Pennsylvania.

Last year's $286.4 billion transportation spending bill -- which Mr. McCain voted against while railing against the $24 billion in earmarks -- contained 423 earmarked road projects for Pennsylvania totaling $707 million. That ranked the state seventh in the amount it received for special highway projects, according to an analysis by the watchdog group Taxpayers for Common Sense.

Mr. Santorum argued this week that earmarks can be important, as he has illustrated by presenting checks all over the state for highway funds. But he said he agreed with Mr. McCain that the process ought to be at least reined in, possibly by requiring lawmakers to put their name next to the special projects in final legislation.

The two senators were also on opposing sides of the 2003 Medicare prescription drug legislation, which Mr. McCain has criticized as a boon to pharmaceutical lobbyists.

Mr. Santorum has received $463,247 from the pharmaceutical industry over the course of his career in Congress. In an analysis by the Center for Responsive Politics, that gave the pharmaceutical industry the 8th highest slot in a ranking of the top industries giving to Mr. Santorum. Pharmaceuticals did not make Mr. McCain's list of top 20.

Despite their differences on some reform issues, Mr. Santorum's staff points out that the senators have developed a working relationship by co-sponsoring more than a dozen proposals together, ranging from designating the month of May as military appreciation month to a ban on partial-birth abortion to Mr. Santorum's "Iran Freedom and Support Act of 2005."

And Mr. McCain is helping Mr. Santorum raise hard money for his re-election campaign. He held two fundraisers for Mr. Santorum in the Philadelphia suburbs in late November, which brought in $100,000.