The specter of civil war is haunting the GOP. You could see the split in the March 17 Illinois Republican primary, where conservative Peter Fitzgerald overtook moderate Loleta Didrickson for the U.S. Senate nomination. More and more these days, conservatives are winning GOP nominations, and moderates are taking a walk.

Didrickson had the support of the Republican Establishment. Didrickson, who supports abortion rights, was touted by Gov. Jim Edgar as ''our best chance to beat (Democratic Sen.) Carol Moseley-Braun.'' Fat lot of good that did her against an opponent who outspent her 7-1 and who labeled her ''too liberal for too long.'' Sound familiar? George E. Pataki used exactly the same slogan to defeat Mario M. Cuomo for the New York governorship in 1994. Only this time, it was used against a fellow Republican.

The warning to Republicans was clear in the March 10 California special election. Republicans insisted it was no big deal for Democrat Lois Capps to win the special election to fill her late husband's seat in Congress. Widows running to replace their husbands have gotten elected to the House 36 out of 38 times.

But Capps's victory carried a larger message for the GOP: Divided, you lose. And, boy, were the Republicans divided. The 22nd District is affluent, moderate and historically Republican. It sent Republicans to Congress for 52 years. But the last Republican to represent the district, Andrea Seastrand, was a hard-line conservative and Newt Gingrich enthusiast. She survived one term.

When her Democratic successor died last fall, the national GOP Establishment anointed state Assemblyman Brooks Firestone as their candidate. Firestone was wealthy, socially prominent and moderate--in other words, very Santa Barbara.

At the last minute, however, upstart conservative Assemblyman Tom Bordonaro decided to run--and got the backing of national anti-abortion groups. Bordonaro pulled an upset and defeated Firestone in the January primary. Add together the votes for the two Republicans, and you get a GOP majority in the runoff. But that didn't happen.

The Democrats targeted moderate Firestone voters who supported abortion rights. ''Being pro-choice is an important ingredient in my campaign,'' Capps said. The Democratic strategy was to reach for the center. And paint the Republican candidate as a tool of the Radical Right. ''This election was driven by local bread-and-butter issues,'' Democratic national chairman Roy Romer said in a recent interview. ''Issue activists from the Far Right put over a million dollars into this district. That didn't sell.''

Moderate Republicans may not be great in number. But they are a swing vote. Especially in affluent suburbs, where voters tend to be economically conservative and socially liberal. Polls revealed that Capps peeled off many of Firestone's primary supporters. ''Picking up one-third of Firestone's voters put her up to 53 per cent,'' Rep. Martin Frost of Texas, chairman of the Democratic Congressional Campaign Committee, observed triumphantly. ''Clearly the divisive primary contest within the Republican Party was a major factor in our victory. We think Republicans are following a path that will lead to their own destruction.''

Randy Tate, executive director of the Christian Coalition--which turned out conservative voters for Bordonaro-- complained about ''a double standard when GOP moderates expect and receive conservative support on Election Day, but those same moderates switch parties rather than support a conservative who wins a primary fair and square.''

Is there a double standard? Absolutely. Conservatives almost always consider a moderate Republican the lesser of two evils. For moderate Republicans, however, the choice is not that clear-cut. Once Bordonaro got the GOP nomination, a lot of Firestone supporters announced for Capps. Firestone himself told Los Angeles Times columnist George Skelton, ''I'll say the unthinkable: This opens up the avenue to a third party.''

He should watch Congress. Moderate Republicans are alarmed over conservatives' holding up financing for the United Nations and the International Monetary Fund (IMF) by adding anti- abortion provisions to the emergency spending bills. Moderates oppose abortion restrictions. They like the United Nations. And they're sympathetic to business leaders who see the IMF as the key to stabilizing the Asian financial crisis.

''If there's someone who worries more about a foreign economic crisis than (about) the principle of U.S. taxpayer money going to repeal right-to-life laws, I haven't met them,'' conservative Rep. John Shadegg, R-Ariz., said recently. Apparently he hasn't met many moderates in his own party.

Now Republicans are giving Democrats another opportunity in Illinois. Moseley-Braun--the only African-American in the Senate--is the most vulnerable Senator up for reelection this year. During the GOP primary campaign, she told a reporter, ''Loleta and I voted very much alike when we were in the state legislature.'' That comment reinforced Fitzgerald's message that Didrickson was ''too liberal.''

Two years ago, Illinois Republicans nominated conservative insurgent Al Salvi over the Establishment candidate, Lt. Gov. Bob Kustra, for the Senate. Moderate Republicans defected and helped elect Democrat Richard J. Durbin. Now moderate Republicans may give Moseley-Braun her only chance to survive.

William Schneider is a resident fellow at AEI.