An admirer asked Mayor Marion Barry last night whether he has a few more gray hairs now than he had at his inaugural 100 days ago. "Yes, but that's all right," said the mayor."My father was completely gray by the time he was 40, so I have heredity working for me."

Chatting casually before the beginning of a dinner given to celebrate his first 100 days in office, he said he is "feeling better than ever" now and has not yet begun to have second thoughts about why he wanted to be the mayor of Washington.

City Council member Betty Ann Kane was less ebullient. "I've survived the first 100 days." she said, "but I won't make any predictions for the 101st."

Sponsored by the Washington chapter of Americans for Democratic Action, the First 100 Days Celebration commenmorated a victory for the small but energetic liberal organization, which is still taking its first steps (as is the District of Columbia) in local electoral politics. In the last city election after a membership vote, the ADA endorsed six candidates, all of whom won.

Beside Mayor Barry, the victorious ADA candidates were City Council Chairman Arrington Dixon and Council members Kane, Hilda Mason, David Clarke and Polly Shackleton, all of whom were present for the beginning of the evening byt left early.

The five Council members departed abruptly after making five of the shortest speeches in political history.

Kane explained the haste in a speech that was slightly longer than those of her colleagues: "I want to thank you all for honoring us, and I think it was very nice to do it on a night when we have a night Council session.Enjoy your dinner and when you finish. come on over to the District Building and see what's happening at the Council meeting."

All five Council members departed shortly thereafter, while John Isaacs, chairman of the local ADA chapter, remarked ruefully in their wake: "One of the hallmarks of the new City Council is that it starts its meetings on time."

Mayor Barry, less pressed, stayed behind to be presented with a T-shirt inscribed "Flaming Liberal" that the local ADA chapter has developed for fund-rasising purposes. "There is some disagreement about how the mayor should dress," Isaacs said. "Some people say he should wear a dashiki and some say a three-piece suit. We have an ideal solution."

"Someday I'll wear it to the office," said Barry. "and The Washington Post will say that the mayor has gone crazy."

He praised the departed Council members for their cooperative spirit. "I think we'll have more than just a honeymon," he said, "we'll have a love feast. We've been together on most issues and when we disagree, we disagree without being disagreeable."

Asked why the Council was being honored with a dinner on the one night of the month when the members would certainly have to leave early, Isaacs said that the key factors were the termination of the 100 days and Mayor Barry's availability.

"Actually, the 100th day is tomorrow," he said. "but Passover begins tomorrow night and we wouldn't want to conflict with that."

Approximately 175 persons bought tickets ( $25 to $75) and most paid extra for drinks at a cash bar. Isaacs said that the dinner was the local ADA's major fund-raising event of the year and, "I hope we will make $3,000."