One hundred years of Democratic dominance of Virginia's General Assembly ended tonight when Republicans gained an agreement that gives them unprecedented power in the House of Delegates.

The pact, which grants Republicans equal representation on committees and allows them to share leadership, came a day after a chaotic opening session in which Norfolk Democrat Thomas W. Moss Jr. was reelected speaker amid catcalls from angry Republicans.

It is similar to an agreement reached in the state Senate in 1996, and puts the GOP on an equal footing in both chambers of the legislature for the first time since 1884. No other bicameral state legislature in the nation has been jointly controlled by two parties since 1966.

"This is revolutionary change in Virginia," said Del. Vincent F. Callahan Jr. (R-Fairfax). "We have achieved a longtime goal, something we've tried for since I got here 30 years ago."

Democrats, who hold 50 seats in the 100-member House, wanted to work out an agreement before Friday, when three new GOP delegates who won special elections this week will be sworn in. Together with the chamber's 46 other Republicans and a GOP-leaning independent, the three new members will give Republicans equality on House votes, which they could use to stop Democrats from passing even simple rules of procedure.

Leaders in both parties acknowledged that they were embarrassed by the ugly scene Wednesday, in which Moss was shouted down by Republicans when he tried to give an acceptance speech. Democrats also were stung by GOP accusations that not allowing the new delegates to be seated before state election officials could certify their victories was unprincipled.

And so House Democrats -- apparently weakened by GOP threats of obstruction and internal dissent among some younger members who fear retribution if Republicans take over the House in 1999 -- arrived today ready to deal.

"You can see it in their faces," said J. Scott Leake, GOP caucus chairman. "They know they've lost. They're just rearranging the deck chairs. Titanic' is the hit of the year. . . . It's happening here in real political life."

"Fairness has prevailed," said Republican Gov. George Allen, who on Saturday will turn over the Executive Mansion to Gov.-elect James S. Gilmore III (R). In his four years in office, Allen saw the House and Senate shift from solid Democratic majorities to parity.

"It's a maturing of the Commonwealth of Virginia from a monopoly to the free competition of ideas," he said. "The people are the winners."

While Republicans hailed the beginning of a new era, resigned Democrats said the agreement was the recognition of the end of another one.

"The last few days will be something all these members can tell their grandchildren, about what they did for the voters of Virginia," said Del. Leo C. Wardrup Jr. (R-Virginia Beach). "It's pure honey."

Del. Thomas M. Jackson Jr., 40, was among a dozen younger Democrats from conservative rural districts who pressed older party lawmakers to share power. For leaders such as the 69-year-old Moss, who are used to dictating terms to the GOP, it was a bitter pill.

"The trust has been fractured between caucuses," said Jackson, of Carroll County, who compared the talks to union negotiations. "We need to rebuild that trust. But the practical side is very, very difficult."

Tonight, Republican leaders approved a Democratic proposal that gives the GOP parity on 19 of 20 House committees, including the new science and technology panel.

Democratic and Republican co-chairmen will head all committees except rules, where Democrats will have an 8 to 7 edge, with Moss as chairman. Each committee will be enlarged, so Republicans can be added without removing Democrats.

If committee co-chairmen decide they cannot work together, they can alternate running the committee from year to year. The power-sharing pact will be void if either party manages to hold 55 House seats at any time over the next four years, but it could continue indefinitely if neither party wins 53 seats.

The new arrangement should be a boon for Northern Virginia, giving the region leadership posts on 11 committees -- including the powerful budget, tax, corporation and courts panels -- up from five chairmen now.

Callahan, for example, will be co-chairman of the powerful appropriations panel, and James H. Dillard II (Fairfax) will help lead the House education committee.

Republican Harry J. Parrish (Prince William) will become co-chairman of the finance panel, and John A. "Jack" Rollison III (R-Prince William) will help lead the transportation committee. The new technology committee will be led by Kenneth R. Plum (D-Fairfax) and Joe T. May (R-Loudoun).

"It's recognition of a new day," said Del. Whittington W. Clement (D-Danville), one of several conservatives who pushed for power-sharing because of the possibility of a GOP majority soon. "It's the right thing to do. It's 50-50. It's hard accepting it, but it's a fact."

Democrats for decades had an iron-fisted system in which the few GOP members were seated in a corner and had their bills killed at the whim of the speakers.

But in Virginia -- where the GOP won all three statewide offices in November for the first time -- and across the South, Republicans have made huge gains in the last two decades, in part because of tax-cutting, anti-crime campaign platforms and in part because of favorable redistricting.

For Republicans, the day represented relief from years of humiliation and secondary status. Their victory was tempered only by the sense among some that they had given up possible gains in the House in the next elections.

They had little sympathy for Democrats.

"After you've had 'em down on the plantation for 120 years, it's hard to give up control," Republican Wardrup said.

Sen. J. Randy Forbes (Chesapeake), chairman of the Virginia Republican Party, said Moss has upheld a tradition in which Democratic speakers punished Republicans who spoke out of turn on the House floor by raising three fingers -- signaling that the next three GOP bills would be summarily killed.

"They have lived in a system that was constructed as an intimidating system, and the problem is, once you lose that, the bark doesn't have the same bite," Forbes said.

Democratic leader C. Richard Cranwell (Roanoke) said the power-sharing agreement is "a reflection of what the world is. The people of Virginia ought to take some pride in the legislators who came down here presented with a tough situation and made it work."