Independent Democrat Joe Lieberman issued an unflattering critique of Sen. Barack Obama today, saying the Democratic presidential contender has "no record" of opposing his party and building bipartisan coalitions.

Lieberman, a Connecticut senator and a close ally of Sen. John McCain, made the comments the same day that two former Republican Congress members endorsed Obama. In some of his sharpest criticism to date, Lieberman said the Illinois senator had never stood independently and reached across the aisle during his 3½ years in the Senate.

"If there's one public official who has consistently put his country ahead of his party, working across party lines to get things done in Washington, it is John McCain," Lieberman said in an interview with ABC News. "It's not Barack Obama, with all respect."

Lieberman scoffed at the formation today of Republicans for Obama by former Iowa Rep. Jim Leach and former Rhode Island Sen. Lincoln Chafee, saying it was McCain who had spent a career working with people on both sides -- often at some cost within his own party.

"Sen. Obama has no record that I can see of taking on positions that are held by a lot of people within his own party," Lieberman said. "John McCain does that all the time. It's part of the reason it took some while for a lot of Republicans to come to his side. Sen. McCain has worked across party lines on the big issues of our time because he knows, he has no patience for partisan politics and all those games."

The nascent Republicans for Obama movement won't have Nebraska Sen. Chuck Hagel, who many assumed would be its most prominent potential member. Hagel, rumored to be on Obama's short list of potential vice presidential candidates, will not endorse a candidate in this election, a spokesman told USA Today.

The sharpened emphasis on bipartisanship comes as Democrats and Republicans court independent voters who could hold the keys to the White House.

Lieberman, whom McCain has considered as a running mate, said he was reaching out to Democrats and independents, "who I think may decide this race."

"John McCain is the truly independent candidate in this race," Lieberman said of the Arizona senator.

But Obama and McCain face some peril in bipartisan appeals.

While trying to woo voters in the political middle, McCain risks alienating his Republican base of supporters. If he were to tap Lieberman as the vice presidential candidate, it would enrage a significant segment of the base, especially those opposed to abortion. Lieberman today declined to comment on his own vice presidential prospects, saying he had not discussed it with McCain.

As for Obama., as Lieberman's comments make clear, the Illinois senator invites analysis of a thin bipartisanship record that might not be terribly flattering.

Lieberman's comments came after a town hall rally of McCain supporters at the cavernous York Expo Center. McCain arrived in a highly choreographed appearance that began with his fabled campaign bus, "The Straight Talk Express," driving into the hall as the theme from "Rocky" blasted from loudspeakers.

On stage, McCain and Lieberman joined former Pennsylvania Gov. Tom Ridge with whom McCain has been campaigning across the state since Sunday night.

But McCain got a politely delivered, thinly veiled reproach from a conservative in the crowd, who suggested he'd gone too far with the effort to reach out to Democrats.

Speaking during one of the senator's largest ever town hall meetings, a woman asked whether McCain would be the kind of conservative "to fight the war of socialistic programs promoted by Sen. Obama and the Democrats?"

McCain took a deep breath, and the crowd laughed as he answered with a smile: "Yes."

The exchange illustrates the fine line McCain has walked in his political career -- and now must navigate in his presidential campaign -- as he seeks to keep the conservative base while also attracting moderate voters.

All this friendly talk of bipartisanship is like scraping nails across a chalkboard for some right-wing conservatives who are critical of efforts like campaign finance reform, a cause that the Arizona Republican championed for and that he is most vividly represented by with the eponymous McCain-Feingold Act.

It's officially titled the Bipartisan Campaign Reform Act. The "Feingold" of the popular title, by the way, refers to Wisconsin's Russ Feingold, a Democrat who is one of the Senate's most liberal voices. Feingold also was one of 23 who opposed a resolution to authorize the use of force against Iraq in 2002 and the only senator to vote against the USA Patriot Act.

After the question about his conservatism, McCain deftly shifted to an area the conservative right can embrace without hesitation: the Supreme Court.

McCain said the next president would get two or three nominations. He talked of his support for the nominations of both Chief Justice John Roberts and Associate Justice Sam Alito -- drawing loud applause -- and pointed out that Obama had voted against both.

McCain promised he would nominate judges who "have a clear record of strictly adhering to the Constitution and who do not believe in legislating from the bench."

Still, McCain consistently emphasizes his record working with Democrats, even to sometimes hostile audiences. The reason is clear: McCain and his supporters -- including Lieberman -- believe his approach and record will resonate with independents and some of the 18 million voters who backed Sen. Hillary Clinton, D-N.Y., during the Democratic primaries.

"I will make this prediction with some confidence," Lieberman said. "Sen. McCain will not just get a majority of independent voters on Election Day, he will get many more Democratic voters -- including voters that supported Hillary Clinton -- than Sen. Obama will get Republican voters. That ultimately is the test of bipartisanship."

During an appearance Monday in Erie, Pa., McCain argued that to make Washington work, partisan affiliations need to be put aside and leaders need to "sit down together, Republican and Democrat, and put our country first. People aren't putting their country first," McCain said. "They're putting their party first."

This is a key theme for McCain, as he seeks to portray himself as the real "change" candidate who can end the bitter partisan debate in Washington.

ABC national correspondent Jan Crawford Greenburg reported from Pennsylvania and producer Howard L. Rosenberg reported from Washington.