At 3:30 p.m. yesterday Sen. John Warner's office telephone rang once. Then a low-pitched female voice began speaking, to the accompaniment of a faint mechanical hum.

"Hello," said the recorded voice. "This is Senator Warner's office. Due to the long Labor Day holiday, there is no one in the office at the present time to receive your call . . . Thanks for calling and have a pleasant holiday."

Warner wasn't alone.

A Who's Who in Washington could have been published on the back of a postcard yesterday afternoon.

Three days ahead of the Labor Day holiday, the nation's leadership had deserted a hot, muggy capital, leaving federal agencies, city businesses and organizations in little-known -- and sometimes unwilling -- hands.

Washington Post reporters yesterday searched for the city's elite and found the expected: skipping out of the office has become a summertime ritual in the city.

To be sure some leaders were in town. CIA Director Stansfield Turner was "in conference." FBI Director William Webster was "tied up" and Secretary of State Cyrus R. Vance was greeting a foreign dignitary.

Of the 67 politicians, bureaucrats and business leaders Post reporters attempted to contact yesterday afternoon, only 15 could be found working in their offices.

Those who did get out of town yesterday were Jimmy Carter (gone fishing in Plaines, Ga.), Vice President Walter Mondale (in China), every cabinet member but Vance and Energy Secretary Charles W. Duncan, Speaker of the House Thomas P. (Tip) O'Neill, Chief Justice Warren Burger, National Security Adviser Zbigniew Brzezinski, senators, congressmen, bureaucrats, businessmen and just about everyone else who could drive, walk or crawl.

Leaving work early on Friday afternoons, consumer activist Ralph Nader told a reporter last week, "is becoming institutionalized. They no longer look sheepishly over their shoulders as they are leaving." Once the boss is away, Nader added, "everyone else goofs off."

Ralph Nader was not in his Washington office yesterday.

"We have a general policy of not giving our his schedule or his whereabouts," Nader assistant Kerry Barnett said.

Others left in charge of deserted offices yesterday were more forthcoming about their bosses' whereabouts.

Defense Secretary Harold Brown spent yesterday vacationing in Newport, R.I., playing tennis at the plush U.S. Naval War College.

Pentagon officials said that while a lazy summer day might seem like the perfect time for a sneak attack, "the secretary is in a position where he could be in touch with the office almost immediately."

Brzezinski was "up New England way," according to his secretary. Next in charge, David Aaron, was in China with Mondale. Who's in charge? "Ambassador Henry Owen," the secretary replied. When asked to identify Owen, the woman answered, "I don't know."

Treasury Secretary G. William Miller was "in Maine somewhere," according to one department official. Next in charge yesterday was fifth-in-command C. Fred Bergsten who said there was nothing to worry about.

"We maintain a close watch over the exchange markets," he said, "and we are prepared to take any action required" to defend the dollar.

Labor Secretary Ray Marshall was flying back from Israel yesterday, while Secretary of the Interior Cecil Andrus was "probably out fishing," according to an aide. Undersecretary Jim Joseph was away, too.

"I love it!" said acting secretary Leo Krulitiz, third-in-command. "It's no problem at all."

District of Columbia Mayor Marion Barry was on his way to Hartford, Conn., yesterday for a political appearance, then planned to spend a few days in Woodstock, Vt.

Potomac Electric Power Co. President W. Reid Thompson was on the beach in North Carolina, Amtrak President Alan S. Boyd was "unreachable," Capitol Centre chairman and Bullets owner Abe Pollin was in China and Washington Metropolitan Area Transit Authority General Manager Richard S. Page was in Cape Cod, Mass.

Nobody seemed to know where John R. Tydings, executive vice president of the Washington Board of Trade, was yesterday. Depending on which of his assitants was quieried, Tydings was either at home "taking a well deserved day off" or in Nova Scotia.

Federal Reserve Board Chairman Paul Volcker skipped out at 2:40 p.m. yesterday. "I will not tell you where he has gone, he cannot be reached," said secretary Catherine Mallardi, Second-in-command, vice chairman Frederick Schultz, said Volcker goes to New York every Friday to be with his family.

George Meany, president of the AFL-CIO, was at his Bethesda, Md., home yesterday. His assistant was on vacation and secretary-treasurer Lane Kirkland was out.

"I'm the highest-ranking AFL-CIO officer here today," said Allen Zack, assistant director of public relations. Zack is number 41 in the chain of command.

"It's so dead, there wasn't another car on the East Capital bridge when I came to work this morning," Zack said.

Housing and Urban Development Secretary-designate Moon Landrieu has not been sworn in yet, and current Undersecretary Jay Janis "was on travel" yesterday according to his secretary.

In other words, the secretary to the undersecretary who is the acting secretary wouldn't say where her boss had gone.

Fourth-in-line Robert Embry said it wasn't unusual for him to be in charge. "This isn't like the Defense Department, where there have to be snap decisions," he said confidently. "Very few things happen that can't be held over until the next day."

President pro tem of the Senate Warren Magnuson was in Washington State yesterday, leaving press officer Gretchen Kiehn in charge.

"It's wonderful," said Kiehn. "Except for the weather. The weather is the pits."

Who was in Washington yesterday?

Attorney Edward Bennett Williams, owner of the Washington Redskins and the Baltimore Orioles, was in a meeting.

Hardware magnet John Hechinger was touring one of his stores yesterday, Georgetown University Hospital Administrator Charles O'Brien was studying films of hypertension, while Kennedy Center Board of Trustees Chairman Roger Stevens was "working hard."

"I usually work Saturdays, too," Stevens added.

Vance -- the highest ranking bureaucrat in Washington yesterday -- was meeting with the Rumanian foreign minister while Alexandria City Manager Douglas Harman was answering angry phone calls about trash containers in the city.

"You can never tell when you might have a snow emergency," Harman said.

Prince George's County Executive Lawrence Hogan was working yesterday. So was Maryland Gov. Harry Hughes.

Washington Star publisher George W. Hpyt was in "an important meeting," according to his secretary, who added, "If it's anything like you people, we're here on Fridays till God-knows-when." Washington Post publisher Donald E. Graham was also in his office yesterday afternoon.

Post board chairman Katharine Graham, however, was vacationing in Massachusetts.

Post President Mark Meagher was also out of town yesterday.

"Fridays are not that bad," said Cortland Anderson, one of five company vice presidents. "The phone doesn't ring quite as much except for prying reporters . . . "