There are 19 primaries Tuesday for seats in the Virginia House of Delegates. Of those, a half-dozen Republican contests are of special interest to the state's leaders and political observers.

Those six involve challenges to delegates who defied GOP House leaders last year by supporting tax increases backed by Gov. Mark R. Warner (D). Activists who oppose tax increases vowed revenge against all 17 of the Republican delegates who broke ranks and mounted primary challenges against six of them.

Four of the nine House primaries in Northern Virginia involve challenges to maverick Republicans: Dels. Joe T. May (Loudoun), Robert D. "Bobby" Orrock Sr. (Spotsylvania), Harry J. Parrish (Manassas) and Gary A. Reese (Fairfax).

The challengers -- Chris G. Oprison, Shaun V. Kenney, Steve H. Chapman and Chris S. Craddock -- have received contributions from the Virginia Conservative Action political action committee, which has set its sights on defeating those who supported the tax increases.

The incumbents had three times the cash on hand as their challengers as of March 31. They received major contributions from Leadership for Virginia, an organization that is backing delegates who supported the tax increase.

Political observers say the imbalance in fundraising will make the anti-tax challengers' task more difficult.

"The anti-tax movement is most successful in open-seat contests," said Stephen J. Farnsworth, an associate professor of political science at the University of Mary Washington. "It's much harder to challenge an incumbent, no matter what the political stripe."

In open-seat primaries, Republicans are hoping to field strong Northern Virginia candidates for the November election so that they can increase their 60-seat majority in the 100-member House.

In the 37th District, which includes Fairfax City and part of Fairfax County, former Fairfax City mayor John Mason is running in a Republican primary against Jim L. Kaplan, who works in marketing and lobbying for a financial services firm.

The Democratic primary involves at-large Fairfax County School Board member Janet S. Oleszek and David L. Bulova, a member of the Soil and Water Conservation Board and the son of Fairfax Supervisor Sharon S. Bulova (D-Braddock).

The winner of the general election Nov. 8 will replace Del. J. Chapman Petersen (D), who is not seeking reelection so that he can run for lieutenant governor.

Voters will also decide between two GOP candidates who hope to replace Del. James H. Dillard II (R-Fairfax), who is retiring from his 41st House District seat.

Three GOP candidates are vying for the chance to challenge Del. Stephen C. Shannon (D-Fairfax) in the 35th District.

Democrats in the 45th District, which covers parts of Alexandria and Arlington County, will choose among six candidates. Because the district tends to support Democrats, the winner of the primary will be a strong favorite in the general election, if the Republicans decide to nominate a candidate. Democrat Marian Van Landingham is retiring from that seat.

The downstate races also present intriguing contests. In the district that includes Richmond and Charles City County, Del. Floyd H. Miles Sr. (D) is running against his predecessor, A. Donald McEachin, who stepped down from the House so that he could run for attorney general in 2001.

Warner has supported Miles, while his onetime political mentor, former governor L. Douglas Wilder, is supporting McEachin.

Also downstate, three GOP delegates who opposed the tax package face challenges. The challengers to Dels. Frank D. Hargrove Sr. (Hanover), Leo C. Wardrup Jr. (Virginia Beach) and Harry R. "Bob" Purkey (Virginia Beach) have run campaigns supporting more money for schools and other services.

The chief negotiator for the maverick Republicans, L. Preston Bryant Jr. (Lynchburg), will face challenger Robert Garber, a former City Council member. Freshman Del. Edward T. Scott (Madison), another Republican who supported tax increases, will compete against former pastor Mark Jarvis in the 30th District.