Kathleen K. Seefeldt and G. Richard Pfitzner, who sit next to each other on the dais at Prince William County Board of Supervisors meetings, stood up yesterday and exchanged places.

A few minutes later, Seefeldt asked for the floor and Pfitzner instinctively called on her as "Madame Chairman." The other supervisors laughed embarrassedly and Pfitzner murmured something about "old habits."

Seefeldt, who for six years as chairman of the County Board was widely credited with establishing its reputation for political decorum, was stripped of the chairmanship yesterday by her colleagues. The Democratic supervisor remains on the board representing the Occoquan District.

In a 5-to-0 vote, the board chose Coles District Supervisor Pfitzner, also a Democrat, to replace Seefeldt.

Pfitzner and Seefeldt both abstained.

In a brief statement after the vote, Seefeldt said she intends "to continue to be a very active member of the board." She added, "I've had the experience, and I sincerely hope I haven't missed the meaning."

Pfitzner said afterward: "I will do my best to serve in the same vein as Mrs. Seefeldt has for so many years."

The change in leadership is seen by county officials as foreshadowing a shift in style rather than substance.

Officials have said privately that some supervisors chafed under Seefeldt's leadership because of her heavy emphasis on procedure. They also said that her cool manner had alienated some members of the board, who felt a chairman with a take-charge attitude was needed.

One of the most visible and powerful women in local government in the Washington area, Seefeldt wanted to keep the chairmanship, according to many in the county.

Pfitzner, a 39-year-old lawyer, has said the board needs to take a more active managerial role, especially in dealing with the county staff and locally appointed boards and commissions. He has complained that the supervisors too frequently react to issues, and too seldom initiate them.

In a separate vote, Joseph C. Reading, a conservative Democrat who represents the Brentsville District in the rural western portion of the county, was unanimously selected again as board vice chairman.

Seefeldt, 50, who was elected to the board in 1976 and chosen by her colleagues as chairman in 1979, first learned that the board planned to vote her out from news reports, according to supervisors.

In a tumultuous board executive session in October, the supervisors said, she dressed down her fellow supervisors for what she considered an embarrassing revelation.

Sources on the board and in the county said Pfitzner's original majority consisted of support from four members of the board: himself, Republican Donald E. Kidwell and Democrats Edwin C. King and John D. Jenkins.

Local newspapers have printed dozens of letters on the move to oust Seefeldt, many of them supporting her for another term as chairman. But the original four supervisors against her held firm yesterday and were joined by Republican Guy Anthony Guiffre. Seefeldt would not comment on why she abstained from the vote.

Seefeldt is credited, even by her opponents, with restoring credibility and tranquility to the county after a stormy period in the 1970s, when board members known as the "Four Horsemen" dominated county politics.

Seefeldt's tenure as chairman of the board has been marked by her cordial but businesslike manner in public meetings. County officials say she has gained for the county the respect of leaders around the state.