Guy Draper was quite a sight that night. He paraded through the downstairs hall of the Hyatt-Regency Hotel in a white blouse with puff sleeves, a black vest and a black widebrimmed hat with a long feather. He looked every bit the part of the Fourth Musketeer. But Draper was simply doing his job as a public relations specialist, making sure all was well at the sparsely attended Mardi gras costume birthday party he organized for D.C. delegate Walter E. Fauntroy.

That was last year. Draper has changed his act, along with his clothes. Smartly dressed in a long-sleeved shirt and tie, he has been temporarily installed in a newly painted office down the hall from Mayor Marion Barry in the District building.

On the credenza behind him are a collection of books: "Amy Vanderbilt's Etiquette," "The New Emily Post's Etiquette," "Entertaining in Washington" and "Debrett's Correct Form." On the top of his Mediterranean desk are invitations from the Crown Prince of Abu Dhabi, the Embassy of China and others. Draper is trying to find out which of more than half a dozen invitations to diplomatic affairs should be honored by the mayor of the nation's capital.

Guy Draper came to Washington from Los Angeles in 1960 to attend Howard University. In the past 15 years, he has rousted about as an agent for television stars and football players, an organizer of parties and picnics, a promoter and a public relations specialist.

Now, with a sense of excitement about the city's new mayor, and with that mayor thinking of developing a high profile on international affairs, Draper is trying to convince Barry that what the city really needs is an Office of Protocol and International Affairs. Guy Draper undoubtedly plans to be its chief.

"There are a lot of protocolary procedures, and the mayor and the City Council ought to be correct," Draper said the other day, his voice echoing in his otherwise empty office. "They have to know where to sit, how to address their host and what to do in proposing toasts." So Draper, now acting chief of protocol, has become the administration's resident tutor on what he calls "the technical and finite details of interacting with the diplomatic community."

When Walter E. Washington was mayor there was no office of protocol, but, Draper said, six other major cities-New York, Los Angeles, Houston, San Francisco, New Orleans and Atlanta-have them.

Some of the mayor's advisers are uncertain whether the city should establish one. Draper is now working on a proposal to help Barry reach a decision. In the meantime, he has ambitiously set about demonstrating the advantages of such an office.

In one memorandum, Draper made a pitch for a broad program of diplomatic activities and outlined some of the finer points of the art of protocol. He noted, for instance, that "protocol dictates" he ride in the official sedan with the mayor. That, Draper explained in an interview, was because as protocol chief he would have to make the introductions.

When Draper grew tired of working at the table provided by the city in his office, he hauled in his own Mediterranean furniture. When he was told there was no money in the budget for a protocol office with $36,000-a-year-chief, Draper started looking for ways to raise the money himself.

When Barry returned from his five-nation African tour in late July, he appointed Draper acting chief of protocol and prepared to receive the mayor's first visiting head of state, President Sekou Toure, of Guinea. Draper took charge.He chose the prettiest of the pretty female workers around city hall to act as hostesses.

On the day of the luncheon, he hopped into the mayor's official car, picked up Mrs. Barry, whisked over to Blair House to pick up Madame Toure and then, using a policeman who had accompanied him as an escort "for security reasons," Draper said, he escorted both ladies to the affair.

The 36-year-old Draper comes to protocol through the back door. Among his most notable achievements in the past, he acted as an agent for two Washington Redskins, since gone amid controversy-running back Mike Thomas and wide receiver Frank Grant. Draper, who is not a lawyer, also helped negotiate contracts for television news personalities Jim Vance and Sue Simmons, of WRC-TV 4, and Lark Mccarthy, of WJLA-TV 7.

Draper has also dabbled in local politics, and was recently appointed to the D.C. Democratic State Committee. In last year's Democratic primaries, he supported two of Barry's foes-City Council Chairman Arrington Dixon and Fauntroy. But when the votes were counted and it was apparent that Barry, a surprise winner, would be the next mayor, Draper leaped aboard the Barry bandwagon, in a single, gung ho bound.

He persistently sought a meeting with Barry's then campaign manager Ivanhoe Donaldson, and was given a position as cochairman of the inaugural ball committee.

In that capacity he arranged an "inaugural disco party" as a small adjunct to the regular inaugural dance. With records spun by WKYS-FM disc jockey Donnie Simpson and a battery of flashing lights. Draper said he would turn the open "flag-festooned ballroom" of the Washington Hilton Hotel into a "disco inferno" to make the swearing in of the city's new generation of leadership.

Apparently, they liked his work as well as he did, because for the past five months Draper has done other odd jobs for the administration without being paid.

"I guess I've reached a point in my life where money is not the determining factor," Draper says. "I've reached the point where it is important to enjoy what you do."