Rep. David E. Satterfield III, the conservative Democrat from Richmond who is dean of Virginia's congressional delegation, stunned his colleagues yesterday by annoucning he will not seek reelection to a ninth term.

His decision set off a mad scramble for his 3rd Congressional District seat, a race that could result in the election of the first black to Congress from the Old Dominion, or -- more likely, according to political observers -- add another Republican member of Congress from the most Republican state in the Old South.

The 59-year-old Satterfield made his announcement at a press conference in Richmond attended by supporters who expected to hear a campaign kickoff speech. It was so unexpected that his congressional staff here learned of it at the same time, when administrative assistant R. Gray Armistead read a brief statement from the boss.

Satterfield acknowledged that the threat of serious challengers played a part in his decision.

He and his wife Anne had agreed two years ago he would retire in 1982, he said.

"While I have no doubt that I can be reelected," he said, "I would be asking my friends for a large investment of their energy, time and money in an all-out campaign in order that I might serve one more term in Congress. iIn good conscience, I cannot ask them to do so much for so little in return." i

Satterfield also expressed disillusionment about "the dramatic changes in the operation of Congress in the last 15 years. He has been frustrated by five-day-a-week sessions that prevent him from spending much time in his home district, by unpredictable schedules that "render personal planning impossible . . . time-consuming votes of no consequence, such as votes to approve the journal of the House," and conflicts among subcommittee meetings "where the real legislative work is done."

Growing demands by constituents on "a conscientious congressman consume every spare moment . . . (and have) removed opportunities for relaxation and virtually eliminated family life," he said.

Two possible candidates quickly claimed credit for the early retirement of Satterfield, who has not faced a serious challenge since he beat the late Richard Obenshain and a liberal independent in a tough, three-way race for a first term in 1964.

State Sen. L. Douglas Wilder, 49, the only black in the Virginia Senate, said yesterday that Satterfield "would have stayed another twho years" had it not been for his public statements that he was considering challenging Satterfield for the Democratic nomination.

Chesterfield County Supervisor Joan Girone, 52, announced last Wednesday that she would seek the Rep ublican nomination in the May 13 GOP primary. "In my speech, said 'Come home, Congressman Satterfield, we haven't seen you in 10 years,' but I didn't expect such fast action," she said with a laugh yesterday.

On Capitol Hill, the news produced shockwaves, especially on the House Veterans Affairs Committee, where because of the earlier announced retirement of Rep. Ray Roberts of Texas, Satterfield was in line to become chairman had he won this fall.

While Wilder said Satterfield's withdrawal "enhances the possibility" that he will run, others suggested that Wilder had been counting on a three-way race to win the seat. They theorized that Wilder could probably win the Democratic nomination on the strength of a solid black vote in the city of Richmond, thus forcing Satterfield to run as an independent. With Republican Girone also in the field, that would have split enough votes to allow Wilder to win. These same observers said that Wilder would be a longshot in a two-way race with a white conservative opponent.

Wilder said "God knows" it would be historic if Virginia sent a black to Congress. He conceded that the decision will rest largely with white suburbanites, who not only make up 75 percent of the district, but also control the money he would need for the race.Wilder won't make a decision until the legislature adjourns March 8 and he has time to "see who comes into the water with me, whether it will be fish or shark."

Except for sending Satterfield -- one of four Democrats in Virginia's 10-member deleation -- to Congress, 3rd District voters have been among the most Republican in the state. They gave GOP Gov. John N. Dalton a 4-to-1 majority over Democrat Henry Howell two years ago.

Satterfield's voting record is among the most conservative in the House. He consistently rates 90 to 100 from the right-wing Americans for Constitutional Action and 0 to 10 from the left-leaning Americans for Democratic Action. He has been a staunch supporter of increased defense spending, deregulation of gas, delaying auto emission controls and prohibiting federal funds for abortions. He opposes legislation that would create a consumer protection agency, strengthen labor unions and allow public financing of elections.

His political vies have been so out of line with the majority of his Democratic colleagues that he was twice passed over for subcommittee chairmanships on the Commerce Committee, where he is the fifth ranking of 27 Democrats. On the less prestigious Veterans Affairs Committee, he has been an active chairman of the subcommittee that oversees operations of the 172 VA hospitals.