Commentary by Doyle McManus: There's at least one potential problem for the Republicans: They haven't settled on a unified national message yet — and a quiet civil war is brewing over what, if anything, it should say.

Republican leaders feel good about their chances for big gains in November's congressional elections, and they should. Polls show that most voters don't think the Democrats' stimulus plan has helped the economy and are ready to try something different. Charlie Cook, publisher of the Cook Political Report and Washington's chief prognosticator of congressional elections, predicts that unless the economy turns around, the GOP will probably win the 39 seats it needs to take control of the House.

But there's at least one potential problem for the Republicans: They haven't settled on a unified national message yet — and a quiet civil war is brewing over what, if anything, it should say.

In one camp are House conservatives, led by Rep. Eric Cantor, R-Va., the House minority whip, who argue that Republicans won in 1994 because the Contract with America laid out by then-Rep. Newt Gingrich, R-Ga., articulated a coherent message around which candidates and voters could rally. The document got wide buy-in from congressional Republicans, with only two members of the House electing not to sign it.

Without that kind of clear, near-unanimous statement, Cantor and his allies argue, Republicans leave themselves vulnerable to being painted by Democrats as the "party of no" — and, worse, as the party that voters rejected in 2008.

Other Republicans, reportedly including Senate Minority Leader Mitch McConnell, R-Ky., worry about finding a tent large enough to include all GOP viewpoints. Trying to come up with a single platform, they believe, could be divisive, and the party should simply embrace a few broad issues such as cutting taxes and spending. We're already winning, they argue; why get too specific and give Democrats a clearer target to shoot at?

There's a practical reason to embrace that argument. In a year when "tea party" activists would like to see the GOP embrace ideas as radical as abolishing the Internal Revenue Service and privatizing Social Security, articulating an agenda that can please every camp is difficult.

That isn't stopping House Minority Leader John A. Boehner, R-Ohio, from trying. He has asked his lieutenants to work on an agenda that most House Republican candidates, incumbents and challengers alike, can run on. But it's likely to be a cautious, consensus document; at this point, even its tentative title — Commitment to America — is tepid. And so far, Republicans seem more likely to embrace an approach to governing rather than specific policies.

"We need to demonstrate two things," said Rep. Kevin McCarthy, R-Calif., who's running the message project. "One, that we learned our lesson from the time before. Two, that we actually have the ability to govern."

This spring, McCarthy launched a glossy website, called America Speaking Out, to invite ordinary voters to send their ideas to the Republican leadership. The website, predictably, attracted a populist jumble of mainstream conservatism (lower taxes, tougher immigration control), Internet libertarianism (decriminalize marijuana, stop limiting abortion rights) and pranks. The outpouring is unlikely to have much influence on an actual platform. Instead, McCarthy and others will assemble in Congress' back rooms in September to try to hammer something out.

The agenda will probably focus mostly on one issue, the economy, and it will try to reinforce the basic message the GOP has already been trying to convey: that the Democrats' policies have failed, and that cutting taxes and spending will work better. The question will be whether the GOP can agree on specific proposals that can convince voters they'll do better than the Democrats.

"There really is only one issue: the economy," said David Winston, a Republican pollster who is advising Boehner. "It's not that healthcare and other issues aren't important, but the economy is the emergency that people want someone to address now."

Winston argues that the GOP should articulate a specific plan, but he also cautions against putting too much into it.

"One of the reason the door has opened for Republicans is that President Obama has focused on so many other things," he added. "If you create an 87-point agenda, you're making the same mistake."

But even getting specific on a few things may be tough at a time when the party stretches across a wide spectrum of ideology. Rep. Paul D. Ryan, R-Wis., a Cantor ally and the intellectual firebrand of House conservatives, has proposed a fiscal "roadmap" that would eliminate all capital gains taxes and the corporate income tax, and replace Medicare with federally subsidized private health insurance for anyone under 55. But Boehner wouldn't sign on.

Boehner himself ran into criticism last month when he proposed raising the age of eligibility for Social Security from 67 to 70 and reducing Social Security benefits for high-income recipients.

"It's not easy to do this," Winston said. "You have to find a direction that encompasses both the tea party and the middle. That's hard to do."

No matter what happens in November, we will have a divided government. If Republicans win a majority in the House, they will still be dealing with a Democratic president and, probably, a Democratic Senate. If Republicans fall short in the House, they may still reduce Speaker Nancy Pelosi's majority enough to make bipartisan deals possible in the middle.

In that divided-government future, it would be a good thing if November's elections produced a mandate for something specific, but that can only happen if Republicans and Democrats alike lay out specific agendas. The all-too-likely alternative is two years of partisan gridlock.

Doyle McManus is a columnist for The Los Angeles Times. Readers may send him e-mail at doyle.mcmanus@latimes.com.