Split by a "revolutionary" call to arms from a small but zealous band of younger House conservatives, congressional Republicans are taking sides in a generational and ideological power struggle that rivals the more famous identity crisis of the Democrats in its importance and immediacy.

The conflict in both parties involves clashes between new ideas and old, with a view in part toward winning over the politically rootless baby-boom generation now dominant in national politics.

But the GOP fight goes farther, catching the party in power at a critical moment, just as President Reagan is putting together a second-term program that Republicans contend could bring on a political realignment that would keep them in power for decades.

It is a crusade to shape Reagan's second term and to emerge as its heir.

For the present, the struggle also could influence government policy on critical issues ranging from tax burdens to relations with the Soviet Union, with the rebels generally taking a more confrontational position than the party's establishment figures.

At the center of the conflict is Rep. Newt Gingrich (R-Ga.), the insurgency's high priest, whose barbed rhetoric has set its tone.

One leader on the other side is Senate Finance Committee Chairman Robert J. Dole (R-Kan.), who has said a tax increase may be necessary to reduce the federal deficit. Gingrich calls Dole the "tax collector for the welfare state."

Another figure on the moderate side is David A. Stockman, director of the Office of Management and Budget, who also says a tax increase may be required and who last week gave the president new, higher deficit estimates that support his point. Stockman, Gingrich said in an interview last week, "is now engaged in Phase One of the terrorization of the president."

It may be that "we are the real Gary Hart," said Gingrich, 41, a former college professor and transplanted Yankee from the Atlanta suburbs, in contending that the Republican Party can eclipse new-wave Democrats like Hart in attracting young voters if it embraces his group's ideas and strategies.

Its ideas include junking the "welfare state" in favor of a "conservative opportunity society" of low taxes, lean government and encouragement of private enterprise.

Their strategies are basically confrontational, although they would embrace cooperative efforts with like-minded Democrats on such issues as tax simplification and military reform, according to Gingrich. "These new-ideas Democrats are very exciting people," he said.

Nettled and in some cases angry Republican elders have responded by suggesting that Gingrich's group is jeopardizing, for the sake of "self-aggrandizement" and "ego-gratification," accommodations needed to pass Reagan's second-term program.

Dole and others argue that Gingrich and his followers, by putting their faith in the supply-side argument that the country can grow its way out of deficit problems, are undercutting support for urgent deficit-reduction measures that may have to include tax increases.

Among some Republicans, there is also skepticism over whether the summons to "revolutionary" action (Gingrich's phrase) is more symbolic than substantive.

For instance, many in the Gingrich group join party moderates in urging more restraint in defense spending than the administration plans and in balking at administration proposals for deep domestic spending cuts destined to be rejected by Congress. They split over such social issues as banning abortion.

Some also wince at Gingrich's attacks on Republican leaders, warning privately that he's going too far.

Foes and skeptics note that Gingrich's "Conservative Opportunity Society" (COS) numbers no more than 15 or 20 in the House, with no comparable Senate following. But they concede that they ignore the insurgency at their peril.

There are several reasons.

The rebels seized control of the platform committee at the Republican National Convention last summer and virtually wrote the party's platform, pushing even the White House farther than it wanted to go in ruling out tax increases.

But Reagan agrees with many of their ideas, especially their opposition to tax increases and support for limits on government, thereby giving them leverage in dealing with skeptical presidential advisers and legislative lieutenants.

They also claim a large -- though disputed -- number of adherents among the roughly 31 Republican freshmen elected to the House this month.

And they are as adept a band of political guerrillas as this town has seen in a long time, making up in audacity what they lack in numbers.

Chief among the prospective flash points is a tax increase, which the insurgents oppose as the principal threat to their goal of reining in government and unleashing private enterprise.

The conflict could point the way for the GOP in its post-Reagan era in terms of philosophy, programs and the party's 1988 presidential nomination. The insurgents' favorite as Reagan's successor is Rep. Jack Kemp (R-N.Y.), champion of low-tax, supply-side economics.

Perhaps even more important, the battle could determine whether Republicans can claim an enduring electoral majority after Reagan's years in office. The insurgents say the outcome hinges on whether the party develops ideas for the future; their elders contend that it depends on whether the GOP proves capable of governing now.

But the struggle isn't just ponderous maneuvering and theorizing by ambitious insiders, with overtones of another shootout across the generation gap.

The clash is also producing exceptional political theater during a period of post-election blahs in Washington, far surpassing in barbed repartee anything Democrats have been saying about each other since losing the presidential election.

The upstart backbenchers gained attention last year for guerrilla strikes against such formidable Democratic figures as House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), but Gingrich is now turning his verbal firepower on leaders of his party, some of whom respond in kind.

Listen, for instance, to a little more of what Gingrich has to say about Dole and Stockman.

By holding the door open for tax increases if necessary to reduce deficits, Dole is helping to prop up the "welfare state," even if he doesn't intend it that way, Gingrich said.

"There is clearly a welfare-state wing of the Republican Party that sees itself as running essentially a cheaper and narrower version of the Democratic welfare state," he added, describing Dole as one of its "first-rate" leaders. "If they spent as much energy on trying to rethink and reform the welfare state, it would be a vastly healthier party," he said.

"Up in Minnesota somewhere, he called me the [Walter F.] Mondale of the Republican Party," said a somewhat stunned Dole, who is more accustomed to making such utterances than seeing them turned on himself.

Gingrich is even more acerbic toward Stockman, a onetime ally whom he sees as a mole for preservation of the "welfare state" within Reagan's inner circle of advisers. That conclusion baffles and amuses Democrats who have fought Stockman on welfare-spending issues.

Stockman "convinces everyone we're faced with the sinking of the Titanic, and then he'll try to sell a lifeboat called 'modest post-Mondale tax increases,' " Gingrich said. "It's a clear, deliberate strategy. I think it was cute when he did it the first couple of years, but it's old hat now. We start with leaks, then we go through dreadful speeches, then we have the arguments over economic forecast . . . .

"It's a little like someone who shoots you in the arm and then says you need a doctor and offers his help. You don't need friends like that."

Dole responds that Republicans like himself are too busy trying to pass Reagan's program to indulge in rhetorical civil war. He suggests that Gingrich and his allies enjoy the luxury of being gadflies in the Democratic-controlled House..

"In the Senate, where we have a majority, we have less freedom to run around and stake out positions of our own," Dole said in a recent interview. "We're supporting the president's position; we have to think of votes . . . . While we're passing the legislation, they're looking around for new ideas."

On a less lofty plane, he asked mischieviously what "new ideas" Gingrich is propounding. "Ask Newt about domestic content . . . . Is that a new idea . . . a Republican idea?" Dole said in reference to Democratic-sponsored legislation to protect the U.S. auto industry.

Gingrich, who concedes that he's no ideological purist when it comes to electoral politics, acknowledged that he voted for domestic-content legislation. "I represent two auto plants," he said, adding, "I always ask him, 'Bob, what's your position on wheat?' " As a Kansan, Dole has always taken care of wheat farmers.

Dole, who, like Kemp, is regarded as a possible contender for the Republican presidential nomination in 1988, also took a poke at Kemp's championing of tax indexing, under which income tax rates will be adjusted beginning next year to account for inflation.

"Indexing was my amendment on the [Senate] floor, but Kemp is now sending out a fund-raiser to preserve it. You know, 'Mail me your money and campaign for prosperity.' It's easy to get someone else's idea and run with it," Dole said.

There is disagreement within Republican ranks over whether this internecine warfare is helping or hurting the GOP. Dole professes, with reservations, to believe that it helps. "They're getting attention, they're stirring up some interest . . . that's a plus," he said.

Others are less certain.

Rep. Mickey Edwards (R-Okla.), a conservative who is a vice chairman of the National Republican Congressional Committee, has criticized Gingrich's movement, saying the GOP could have done better in House elections without "confrontation" tactics and a "rah-rah mentality."

House Minority Leader Robert H. Michel (R-Ill.) takes an approach similar to Dole's, implying that the Republicans' first duty in Congress is to back the president's program. "We have a responsibility to govern," Michel said in an interview last week. "You don't have the president winning by that amount [59 percent of the popular vote] and then cutting his legs off from under him . . . . It's great to be out there talking, but we have to deliver."

Some party leaders are more critical of Gingrich and his group when assured that they will not be quoted by name. "Newt's a talker . . . . He couldn't legislate his way out of a paper bag," said one. The whole COS operation is "self-aggrandizement," said another. "Ego-gratification and personal ambition," said a third.