Singer Barbara Cook makes an offstage entrance as a disembodied voice in her concert at the Kennedy Center, and by the end of two bell-like bars has captured the audience, sight unseen. She never lets them go throughout the performance, and neither do they willingly let go of her at the end.

"This is silly," she told us fondly on opening night, after riotous applause had almost drowned out parts of some of her opening numbers. Almost, because nothing, not even the inadequate sound system, can override Cook's tone, power and phrasing.

Early on in the concert one wonders why any amplification at all is necessary, since Cook's voice is big enough to fill the Terrace Theater unaided, whether she's belting out "Sweet Georgia Brown" or tinkling along with "Sing a Song."

The mechanics of her presentation are totally concealed -- swallowed up, rather -- by her talent and capacity; when she rings a change you don't see the bellropes move. The range, timbre and quality of her voice are operatic, and her use of it is always so sure and straightforward it sounds simple.

This musicianship is multiplied by Cook's stage presence, which is simultaneously unaffected, engaging and commanding. At will she transforms the stark and propless stage into now a cabaret, now a concert hall, now an intimate salon where a few friends have gathered. When she ran out of prepared encores and then drew a blank in the middle of a song chosen on the spot, she charmed her way out of this classic singer's nightmare so delightfully it made everyone glad it had happened.

Nothing is so deceptively "natural" as a well-schooled voice. In "Paper Moon" Cook gives us a glimpse of the deep study that goes into her work: She evokes Lena Horne and Peggy Lee and their predecessors in the blues and jazz, then brings the song forward into her own absolutely nonderivative style, all done so smoothly that the echoes fade as they are perceived.

Cook loves intelligent and intricate lyrics, and demonstrates perfect diction in such intricate songs as "Mr. Right Left," written for her by Wally Harper. Harper, a noted Broadway composer, producer, director, orchestrator and conductor, somehow finds time to tour with Cook as her musical director and accompanist. It is a privilege to see a large talent subordinate itself to a larger one for the sake of their mutual art.

Cook sings for an hour or so, and while it's sad to see her leave the stage it's also something of a relief, for she throws that big voice around with such daring that one wonders how long it can last. Strain showed only for one tiny moment during the evening, as she made a full-octave leap in "Georgia Brown."

The bill is filled out by The Manhattan Rhythm Kings, a trio of former New York street singers making their Washington debut. They are fine performers, although a long way from rating as headliners, and set just the right tone in warming up the audience for Cook. Their specialty is upbeat takeoffs on popular songs from between the World Wars, and the treatments are lively and infectious if sometimes repetitive and overcampy. Their "Snap, Crackle and Pop" is a flawless gem. BARBARA COOK -- At the Kennedy Center's Terrace Theater through August 30.