Former Fairfax County Supervisor Rufus Phillips, an international businessman and former Central Intelligence Agency employee from McLean, announced his candidacy yesterday for the U.S. Senate from Virginia.

Phillips, 48, who lost a race for Congress in 1974 and lost his seat on the County Board in 1975, made his announcement in the rural Southside Court House, where he was raised during the Depression and where his mother's family has lived for more than a century.

"Virginia" he said, "needs a new voice in Washington."

A Democrat, who as a supervisor helped pioneer Fairfax County's efforts to control growth during the early 1970s, Phillips joins approximately seven other announced and unannounced candidates for the party nomination to succeed Sen. William L. Scoot.

Scott a Republican elected in 1972, has announced he will not seek re-election. At least four Republicans, so far are hoping to succeed him.

Phillips, who served as Dranesville District supervisor for Fairfax County from 1972 through 1975, describes himself as a party moderate in the tradition of former Sen. William B. Spong Jr., whom Scott defeated five years ago.

"My primary concerns are about people . . ." he said, "but I am conservative about the means we use to help them. I'm skeptical about the standard answer of a new program and a new bureaucracy to administer it.

"We need to make work those programs which are good; we need to eliminate those which can't work and we need to develop new ways of solving problems without spending vast new sums we don't have. We will all benefit when government does fewer things better . . . not more things badly."

A native of Middletown, Ohio, Phillips was raised in Charlotte County, Va., attended Woodberry Forest School and Yale University. He joined the CIA in 1953, left after a year to join the Army, and ended up in Vietnam as a military adviser to the South Vitenamese government.

Phillips remained in Vietnam nearly a decade, with the Army, with the CIA, and finally as the Agency for International Development's assistant director for rural affairs in South Vietnam. Summoned to Washington in the fall of 1963 to report personally to President Kennedy on U.S. operations in Vietnam, Phillips detailed the failure of his own program - a report David Halberstam in "The Best and The Brightest" calls "a remarkable moment in the American bureaucracy, a moment of intellectual honesty."

Phillips is now president of Inter-continental Consultants, Inc., an international engineering firm specializing in airport design.

Since August, Phillips has worked voluntarily at more than 10 different jobs around the state, ranging from meat packing in Lynchburg to coal mining in Dickenson County. He hopes to make it 50 jobs before next summer, he says, in an effort to better understand the problems federal regulation places on small businesses.

"I want to bring Washington to the real world where real people live and work," he said. "I've learned from my work days that government regulation is not responsive to the problems at hand."