Chicago law firm Winston & Strawn, which successfully wooed Walter Mondale for its Washington office, found out it had to accommodate a bit more than just another partner. With the former vice president came the nerve center for a low-key presidential campaign-in-the-waiting -- complete with political strategists, the Secret Service and leftover but prophetic "Fritz '84" buttons.

Winston & Strawn are paying a pretty price for Mondale. The firm won't say how much, but reliable sources say he turned down offers in the neighborhood of a quarter million dollars from other firms.

What he brings as former veep to the law firm is also an unknown commodity. Not too many former vice presidents return to private practice. Hubert Humphrey wasn't a lawyer, and Spiro Agnew was disbarred. Agnew's successor, former president Gerald Ford, has opted for the sand traps at Palm Springs and the rubber-chicken circuit.

The only one comparable is Richard Nixon, who, after his defeat for the California governorship, added his name to New York's Mudge Rose Guthrie & Alexander before running in 1968. A Mudge Rose spokesman refused to discuss Nixon's performance.

But a lawyer familiar with Nixon's days at Mudge Rose said Nixon was a great asset. It wasn't that Nixon brought many clients with him -- except for Pepsi-Cola -- but he brought to Mudge Rose what Mondale might bring to Winston & Strawn -- that ineffable "star" quality found in the uppermost levels of lawyering and politics.

Mondale may perform much as "klieg lights attract flies" the lawyer speculated, bringing in clients who need help at the top of the political/legal world.

One thing is certain: The firm's offices, hard by the Pennsylvania Avenue bridge to Georgetown and well off the beaten law-firm track downtown, have taken on a new look just to accommodate Mondale's presence.

The firm actually played a game of musical offices, making sure the prized newcomer was comfortable.

Senior partner John Reilly says it was only right to give Mondale the biggest office. "I gave it to him so he would be beholden to me," Reilly, a friend of Mondale's for 20 years, said jokingly.

Of course, that meant Reilly had to move. So he bumped partner Edward Meader from a corner office to an interior one. That office has been vacated by partner Richard Williamson, who went over to work in the Reagan White House.

Room also had to be found for an aide Mondale wanted to bring with him, Robert Torricelli, who had been Mondale's special assistant and then a key campaign strategist. Torricelli moved into a vacant office near Mondale's.

An office also needed to be found for Pat Sarcone, who was an executive assistant to former senator John Culver of Iowa, which just happens to be the first presidential caucus state for the Democrats.

Then there is this nonlawyer who hovers around Mondale. That fellow always seems to have his finger on a hearing aid in one ear while apparently chewing on his wrist.

Turns out he's a Secret Service agent assigned by law to guard the former vice president for six months, talking into his wrist microphone and listening for instructions from the main office.

The Secret Service decided it needed a command post at the firm and out went a clerk. The service refused to divulge how much rent it was paying the firm. "Classified," said an agent.

Another Mondale aide, former executive assistant and top political strategist Jim Johnson, has opened a consulting firm, leasing space from Winston & Strawn just down the hall from Mondale's office. Johnson's proximity to his former boss certainly won't hurt when Mondale begins to organize the campaign speeches his aides say he will make for fellow Democrats in 1982.

Those trips may be paid for by the Committee for America's Future, a political action committee set up recently by Mondale to be run by former Mondale aide Rebecca McGowan.

Former Mondale staffers are showing up in law firms or other businesses all over town. Not one of Mondale's inner working team, in fact, has left the area. Dick Moe, former chief of staff, is at Davis, Polk & Wardwell; top aide Gail Harrison is in a local consulting firm; top speechwriter Fred Martin has decided to freelance his talents. And Mike Berman, Mondale's chief counsel and a bit of a Minnesota political junkie who surprised a number of folks by completing a full four years at the Executive Office Building, now is taking care of transition business and is planning to practice law in D.C.

If one didn't know better, one might consider those aides a shadow campaign staff, waiting for Mondale's word on 1984.

Mondale staffers coyly deny any such intentions.

But then there're those "Fritz '84" buttons floating around, printed by a former advance man for a party thrown after the Reagan landslide.