The Virginia House of Delegates' entrenched committee leadership was realigned dramatically and Northern Virginia's 19-member delegation, the largest geographic bloc in the House, was left leaderless by Tuesday's elections.

Democrats and Republicans agreed yesterday that it may take years for any legislator from the Washington suburbs to achieve the power and prestige of House Majority Leader James M. Thomson (D-Alexandria), a 22-year member of the House who was defeated in the elections.

"It's hard ot imagaine anyone else assuming his role," said State Sen. Adelard L. Brault (D-Fairfax). Thomson's counterpart in the Senate. "The citizens of Alexandria did a tremendous injustice to themselves and to all of Northern Virginia in defeating Jim Thomson," agreed Del. Warren E. Barry (R-Fairfax).

The elections also boosted the number of women in the 100-member House from seven to nine: the number of blacks from one to four: and the number of Republicans from 17 to 21. The GOP's net gain of four seats left them short of their 1974 high of 24 House members.

Independents retained three of four House seats they held in the 1977 session, leaving the Democrats with 76 seats, they had 79 before the election.

Perhaps the most drastic changes to result from the election will not be made public until January when House Speaker John Warren Cooke announces assignments to the House committees, but some of the changes were apparent yesterday. Eight of the 12 major House committees will have new chairmen and four of the seven seats on the important Rules Committee will change.

Del. A. L. Philpott, 58, a Southside Virginia lawyer and chairman of the House Democratic caucus emerged yesterday as the heir apparent to Thomson's position as majority leader. Since Cooke has announced that he will retire at the end of his present two-year term, that would make Philpott a front-runner to succeed Cooke.

Until yesterday, most legislators seemed to assume that position would be Thomson's Coode yesterday praised Thomson as a "very able legislator and a very good floor leader" and said his defeat was "a great loss to the state."

Overall, Cooke said, the number of freshman entering the House next year will be 17, a "smaller" than average turnover and one that he predicted would produce "very little change." The legislature's direction, he said, "will be very much th same: progressive, yet moderate.'

Northern Virginia legislators, however, were outspoken over what they saw as the impact of Thomson's defeat and the apparent defeat of Del Thomas Jefferson Rothrock (D-Fairfax), a three-term House member who, along with Thomson, was one of four Northern Virginians on the House Apprepriations Committee. If Thomson had been re-elected, he would have been chairman of the committee, which is largely responsible for reviewing the state's budget and spending programs.

Normally Thomson's job as head of the region's bipartisan House caucus would fall to Del. Dorothy S. McDiarmid (D-Fairfax), who some legislators say is not brash enough that Thomson did. "I don't know if she's pushy enough for the job," one legilator, who asked not to be named, said yesterday.

Others said the expert Brault and Sen. Omer L. Hirst (D-Fairfax), the senior member of the delegation, to exert more influence in the regional caucus at which strategy si planned for such projects such as Metro tranit aid and Northern Virginia toaxing measure.

"I don't think that there's any question it's going to put more on my shoulders," Brault said. Citing his partnership as a majority leader with Thomson, he added, "I'm by myself now."

he apparent 61-vote defeat of Appropriations Committee member Rothrock, by Robert W. Thoburn, an ultra-conservative Republican who is a minister, may make the test of getting more state spending in Northern Virginia more difficult, some legislators said. Furthermore, Thoburn's adament opposition to local tax measures long favored by the delegation makes it unlikely that the Northern Virginia delgation will be harmonious as in previous sessions, they said. Thoburn also opposes ratification of the Equal Right Amendment and believes that abortion should be a capital offense.

"Robert Thoburn has got to be anathema to everything Northern Virginia stands for," said Del. Ira M. Lechner, an Arlington Democrat who is leaving the Assembly, Losing Democratic gubernational candidate Henry E. Howell was more blunt yesterday. In a Norfolk interview, he called Thoburn "the siamese twin of caveman" and predicted he would have difficulty working with other legislators.

With the election of Thoburn, the area's delegation ranges from liberal to extremely conservative in political ideology. Lechner and others said that pulling such a delegation together may be impossible. "There won't even be a Northern Virginia position on many issues," Lechner said.

"You're going to see a significant change in the way that whole General Assembly operates", said Del. Vincent F. Callahan (R-Fairfax), the region's senior Republican. Callahan also described Thomson's defeat as "a loss to Northern Virginia."

The House Appropriations Committee now is likely to be headed by Del. Richard M. Bagley (D-Hampton), who McDiarmid said will be sympathetic to Northern Virginia requists for financial aid for the Metro transit system.

Seven other key House committees also will have new chairman as a result of the election and previously announced retirements. But only one of those groups - House Labor Committe - will be getting a chairman who is markedly more liberal than his predecessor, Del. Robert E. Washington (D-Norfolk), who has supported movees toward collective bargaining, will become chairman of that committee, but as Lechner noted "he doesn't have the troops" on the committee to back his own position.

New chairmen also will be selected for the Privileges and Eleection Committee, which Thomson headed, and and Towns, Corporation, Insurance, and Banking, and Health and Welfare committees.

The House will get two women lawyers - Elise B. Heinz of Arlington and Mary Sue Terry of Patrick County - and a consumer activist, Gladys B. Keating of Fairfax County, as the number of women in the Assembly reaches an all-time high of nine. All who sought re-election Tuesday retained their seats.

As expected, three urban blacks - James Christian and Benjamin Lambert of Richmond and Robert C. Scott of Newport News - will join a fourth, William P. Robinson Sr. (D-Norfolk) in the House.

Republicans gained two of their four new seats in the Lynchburg area and the others in Culpepper and Alexandria. It could have been worse, considering the size of the Dalton victory," Brault said.