"Bless this bus and bless this driver," sang the 14 members of the Fenwick Follies as they settled in their seats, ready to go on the road again.

The tours of the song and dance ensemble, whose members' ages range from 62 to 80, always begin that way, but this day was special -- two performances, an exception to their usual policy of only one program a day.

This morning they were on their way to the Support Center in Wheaton to entertain Maryland native Mary Kirby on her 101st birthday. Despite an earlier commitment to the National Institutes of Health for an evening program, the Follies members decided that the celebration of more than a century of living was too important to miss.

Deriving its name from 1400 Fenwick, the Silver Spring building in which its members live, this senior citizen troupe puts on a well-paced show that underlines solid, old-fashioned values and mixes group singing of well-known favorites with individual specialty numbers.

The ensemble members dress in neat white slacks, red shirts and navy-blue blazers and wear patriotic red and white striped top hats banded by a strip of stars on a blue background. The show starts with the troupe marching in, waving to the audience, behind 75-year-old Max Seidlitz, who is dressed as Uncle Sam.

The performers go through their routines with an easy, unself-conscious good humor. The mood is friendly and the audience is encouraged to join in on songs and dances. Voices may not always hold out, but the entertainers' infectious enthusiasm never falters.

The driving force behind the Fenwick Follies or, as she calls herself, "the big, bad wolf," is Sylvia Denis, the 69-year-old resident manager and social worker at 1400 Fenwick.

"I had to provide activities for all these people," explained Denis. "We had no funds to pay for professional entertainment so I thought the best way was to train our people and find out who has hidden talent -- and who doesn't," she added laughing.

Denis started with small gatherings of building residents where people could perform on an informal basis.

"I discovered a few who were very capable of doing things they'd never done before," said Denis. "It took months and months to encourage them."

One of the troupe's members, 69-year-old Elsie Hopkins, recalled the days when Denis was trying to convince people they could perform for the public.

"Mrs. Denis kept on after me," said Hopkins, whose fervent, unaccompanied singing of spirituals seldom fails to get the audience clapping with her. "I kept saying, 'no, no, no' and she kept saying, 'yes, yes, yes.' Finally, I said I'd try."

Denis assembled a group, rehearsed it until the numbers went smoothly and in June 1974, the Fenwick Follies made its official debut, performing for a B'nai B'rith convention at the Mayflower Hotel in Washington.

Singer Hopkins remembers the occasion well: "I was nervous. I just got up there and stood and looked at them and told them if I made a mistake just to go along with me. After I had eyed them it was all right."

What makes performing all right according to Hopkins and other members, is the appreciation of the audience. "We just love it," said Alice Schuman, who reluctantly admits to being in her seventies. "The people seem to enjoy it so."

On the special day when the group sang two performances, a patient at N.I.H. was so moved by Hopkins' singing that he joined in, later commenting that "she brought tears to my heart."

"We're received with open arms," said Denis. "We get requests all the time to come back. None of these people has exceptional talent, but it's the way they do it."

There is a special directness of communication in what the group does because the worries about making a mistake are gone. The foremost aim is to share. With particular understanding the chorus will direct to older audiences such standards as "Give My regards to Broadway" with its line about 'yearning to mingle with the old time crowd."

Included in the specialty numbers are Spanish songs by a quartet of Cuban exiles who bring their heritage to others with the music. Magda Forrest, who came to this country in 1923 calls up early days on the other side of the Atlantic when she does a polka from her native Sweden. Chorus member Betty O'Neill makes a point of going over less mobile members of the audience when she sings. She herself has just recovered from a slight stroke in December.

Earlier this month, the Fenwick Follies marked its 100th program with an appearance at a Rockville nursing home. For six years the troupe has volunteered its time to entertain at hospitals, nursing homes, clubs and churches throughout the area.

Its efforts received a needed financial boost recently when the group was awarded $500 by the Montgomery County Arts Council for costumes and transportation assistance.

(The award was made under the council's new grants program, which also presented $500 to Glen Echo Dance Theater and $250 each to Montgomery County Masterworks Chorus, Opera Casalinga, the Maryland Youth Ballet and the Boyds Arts Committee.)

"I couldn't ask for a better group of people to work with," said Denis as she considered the last half-dozen years. "My goal is to get my group on Broadway -- and you can print that," she added, with a laugh.