"A friend of a friend of a friend asked me if I would do this, and I said I would be glad to help out," explained John Coleman, who was host yesterday to the crowd of 110 at his newly renovated Fairfax Hotel. The Sunday brunch at the hotel's Jockey Club restaurant was for the Van Cliburn Foundation, sponsor of the international music competition, and in honor of the tall. still-youthful-looking 44-year-old pianist from Texas.

It was also a "thank you" for all the traveling Texans and Washington-area arts aficionados who had worked on Saturday's post-concert reception for the 1977 Cliburn silver-medalist Alexander Toradze and the visiting Moscow Philharmonic.

Coleman himself, as well as guests Ina Ginsberg and Sen. Larry Pressler (R-S.D.), had not attended the performance of the preceding evening, but there was no lack of enthusiastic reports to fill them in on the event.

"It was a fabulous concert," said Dale Miller, whose wife, Scooter, was the primary organizer of the afterconcert event.

"Sensational concert," echoed Martha Hyder, former chairman of the Van Cliburn Foundation.

"We're working very hard on this tour, but it's fun," Hyder continued. "This is all part of the followthrough we provide for our contestants. We do all the extra things -- free publicity, managerial advice. They all get love and tender care."

Competition committee members weren't the only ones who saw to that on Sunday. When Toradze and Cliburn arrived, the Roger Mudds, Anatoli Dujev (the Soviet Embassy's cultural counselor), Patrick Hayes and Katherine Filene Shouse moved through the crowd to greet them.

The round-faced, smiling Toradze charmed every one of the celebrites rushing to meet him. He was at first somewhat reluctant to pose for photographers, but took their orders with a good-natured shrug as cameras materialized from the crowd.

Cliburn himself was content to take a back seat to the Russian medalist from the American competition named in his honor.