Political moderates predominate in the U.S. electorate, but the two parties are increasingly captives of their extremes. Will the moderates ever rise up and assert themselves?

In the Republican Party, they ought to do so by defending Senate Majority Leader Bill Frist (Tenn.) against right-wing attacks for bucking President Bush (and Christian conservatives) over embryonic stem-cell research. [IMGCAP(1)]

Republican moderates also ought to start speaking up for “emergency contraception” before the right makes banning it a litmus test of party loyalty.

Someone in the GOP ought to tell Bush that “intelligent design” is not a true scientific theory on a par with evolution. And moderates need to fight at the state level to prevent “ID” from being required teaching in biology classes.

Except for Log Cabin Republicans and the Republican Unity Coalition, does anyone in the GOP dare to come out for civil unions for homosexuals and to resist the party’s reliance on gay-bashing to win elections?

It’s almost impossible for a pro-choice candidate to get the GOP presidential nomination, but anti-abortion mania could be the undoing of the party in the long run if Bush installs a U.S. Supreme Court that actually overturns the Roe v. Wade decision, as the religious right expects him to do.

If current nominee John Roberts proves to be a vote against Roe, it will take only one more rightist appointee to ignite struggles in every state to ban abortion. Polls show that two-thirds of the electorate wants Roe to remain the law of the land.

There’s no question that the Democratic Party is just as much captive of the left as the GOP is of the right. Unions, pro-choice feminists, trial lawyers and civil rights liberals call the shots.

America-basher Michael Moore was lionized at the last Democratic convention. MoveOn.org is a major party mouthpiece. Leftists dominate the Democratic blogosphere. And Howard “I hate Republicans” Dean is party chairman.

But the Democratic Party has an influential moderate wing, led by the Democratic Leadership Council, with which a number of 2008 presidential candidates are affiliated, including frontrunning Sen. Hillary Rodham Clinton (N.Y.).

There is no real equivalent in the GOP that can serve as an organizational and intellectual base for moderate candidates like former New York Mayor Rudy Giuliani, New York Gov. George Pataki and Sen. John McCain (Ariz.).

Moderate groups like the Republican Main Street Partnership are useful, but they are not powerful, and moderate office holders are regularly targeted for defeat by arch-conservatives from the Club for Growth, the Free Congress Foundation and the religious right.

Occasionally, a Republican moderate will speak out in a provocative op-ed, as when former Sen. John Danforth (Mo.) charged that “Republicans have transformed our party into the political arm of conservative Christians.”

But Danforth, an Episcopal minister, has no organizational backup. And, while his articles gained some momentary attention, they sparked no moderate rally.

Moderates need to organize and fight — in both parties. When they don’t, they ill-serve a centrist public and miss a political opportunity.

A July NBC/Wall Street Journal poll showed that a plurality of voters, 39 percent, regards itself as moderate, compared with 33 percent who say they’re conservative and 22 percent who say they’re liberal.

A new Pew poll shows that the public supports embryonic stem-cell research by 57 percent to 30 percent, and that 53 percent favors allowing gays to enter legal arrangements giving them the same rights as married couples.

There is no new polling on contraception, but I would be shocked if its availability were not overwhelmingly supported by the public.

Yet the Bush administration is balking at approval of the “morning-after pill,” which prevents a fertilized egg from attaching to the uterine wall.

Even though this is a process quite distinct from abortion, the religious right is hostile toward the drug, and that opposition has led two potential 2008 candidates, Pataki and Republican Gov. Mitt Romney of Massachusetts, to veto bills to make the pill available without a prescription.

Frist, who is pro-life on every other matter, nevertheless came out for federal funding of stem-cell research requiring the destruction of embryos “left over” and destined for destruction at fertility clinics.

Despite all he’s done for the right — including making it virtually certain that Bush’s judicial nominees will get approved — Frist is now being attacked for his stem-cell view.

The right insists that life begins at conception and that therefore abortion and embryonic stem-cell research constitute murder.

Yet, if this were truly the basis of its belief, fetuses should be baptized as soon as it’s clear a woman is pregnant and miscarriages should be the cause for a funeral and a religious burial.

No moderate would say that destruction of a human embryo is of no moral consequence — it constitutes a potential human life — yet there’s ground for suspicion that some religious conservatives are as much about punishing illicit sexual activity as they are about saving “life.”

The religious right has every right to be politically assertive. So does the secular left. What’s needed is for moderates to get militant and contest these extremes.