THE evidence is piling up that folks of all ages and disparate backgrounds are hankering after meaningful lyrics set to artful melodies driven by a swinging beat. Vocalist Deater O'Neill points to her two younger sisters who "all of a sudden love to hear music with lovely melodies and good poetry" and observes that "the older generation that lived through the years when all these standards gained their initial popularity, they're appreciating the return of just good love songs and good dancing material." Beverly Cosham says that she herself sings "songs that will demonstrate some sort of emotion, that do something to touch the audience and have some universal feeling that a lot of times people don't want to get in touch with because they don't want to bare their souls."

O'Neill currently sings with her nine-piece band Sundays at the Top O' the Town, Rosslyn, and with her trio Mondays at the Pirates' Hideaway in Georgetown. She will be the featured entertainer with a 17-piece orchestra at the Cherry Blossom Festival Ball on April 9 in the new D.C. Convention Center. Cosham will remain at Dot's Spot on Capitol Hill every other Friday and Saturday through August. Both singers draw from the works of the older songwriters but sprinkle in songs of the last decade or so. Cosham names Harold Arlen, Yip Harburg (whom she met shortly before Harburg died in 1981) and Stephen Sondheim as favorites; O'Neill, the Gershwins, Cole Porter and Michel Legrand.

An avowed "flower child" of the late 1960s, O'Neill dropped out of University of Michigan opera studies to go on the road as Jeanie in "Hair" and then joined the Tennessee Blues Band as lead vocalist. Pursuing the classics once again, but in a desultory fashion, she stumbled upon the 1940s style Starlight Orchestra one night and that was it. She joined it for a couple of years here in Washington where it frequently appeared in the Shoreham's Blue Room, once with the late Charlie Spivak as guest trumpet player and on another occasion alternating with a small combo led by trumpeter Billy Butterfield.

Not long ago O'Neill was called upon at the 11th hour to fill in for the ill vocalist of the Larry Elgart Orchestra on a college date in Pennsylvania and last summer she helped open a jazz room in Honolulu owned by former Stan Kenton saxophonist Gabe Baltazar.

"I have really dibble-dabbled in everything," she says, adding to the already motley list her five years as soloist at a Methodist church in the District, a National Public Radio appearance in "Medea's Dream" ("the last operatic thing I've done--staged in a shower, a real kick") and jazz gigs at Mr. Y's Lounge and the Black Force Tavern. O'Neill, who grew up in Michigan, has divided the last dozen years about equally between the District and Alexandria.

At those Sunday evenings at the Top O' The Town, a dance set alternates with a show set, O'Neill clarifies, the latter "a 60-40 combination--40 percent being some old standards or some of today's, things that people are very familiar with, and for the 60 percent I'm doing, for example, George and Ira Gershwin's 'They All Laughed,' but with the verse, bringing back some marvelous songs and their verses. And not only do I have great musicians that I can call on for dynamite solos, I have the marvelous arrangements of my alto player, Mike Crotty."

Cosham, a D.C. native and graduate of Western High School (now Ellington School of the Arts), also is of an age to have been exposed to massive doses of rock music but she was not infected. "It was very interesting because the guy I dated when I was in high school and college was very heavy into Lambert, Hendricks and Ross, and that was very avant-garde for high school kids because you were supposed to be doing whatever Dick Clark was doing. But we used to sit around and listen to Annie Ross and just marvel at the sound of that group. And that made me more interested in things like what Ella Fitzgerald was doing."

Formal instruction in music never has been a part of Cosham's background, although she has been singing since she was 4 years old. "I can remember singing stuff like, 'Caldonia' and whatever else I heard on the radio, and then in school I did a lot of lead stuff with the chorale. I have this great desire to sing 'Carmen' but I never did have any training. I have taught myself to read music and pick out chords on the piano because I prefer to know. And then listening to people like Mabel Mercer, Frank Sinatra and Johnny Hartman I have learned phrasing and enunciation and evolved the style that I have."

Recently she has spent a lot of time in New York gigging in clubs and traveling a "mini-circuit" of caberet venues from Baltimore to New Haven.

"Pain songs" make up part of Cosham's repertoire and she says it impresses her that people come up after a performance and ask her for a copy of the lyrics of certain songs. "They'll say things like, 'Gosh, how did you know I felt that way?' or 'Those were the words I was trying to get to.' Or I have people crying. To me, to be on stage first of all, you're there to entertain, but I want the people to feel something. So what I do on stage is to create this little bit of reality that lets these people step in for 45 minutes and say, 'Okay, I'm now gonna feel all these things that for all day I have not allowed myself to feel.' "

But lest it be thought that she sings only about pain, she points out that songs like "Beautiful Sadness" play a big role in her act. It concentrates on the "good things" that a dissolved love affair can be remembered for. "I have people in Baltimore, in New Haven who--everybody wants these lyrics and I'm going to have them Xeroxed!"