AN UNUSUAL SUSPENSE novel that turns on a woman's search for her own identity comes from Margaret Yorke, who has been published in England and makes her American debut in The Come-On (Harper & Row, $8.95). Here is a writer who can deal with subtleties of character, meanwhile building suspense to a breaking point.

Kate Wilson is a colorless woman in her early middle-age. She works at an unexciting job as a receptionisttypist for a group of doctors in a clinic. At home, she is dominated by a mother who fakes illness and delights in ringing for Kate just at the moment her daughter's favorite musical program is about to begin on the radio. But, on certain weekends, Kate escapes her drab existence and becomes Mrs. Havant, an attractive widow enjoying a holiday at a quietly luxurious hotel. One of the doctors chances to discover her secret, and the two share an undemanding, thought tender, love affair.

Then, on one of those escape weekends, Kate stops to help a young woman change a flat tire and leaves as another good Samaritan arrives to finish the chore. When the same woman is found raped and murdered in her apartment, Kate is the only one with a clue to the killer's identity. He realizes it and begins a search for the tall woman in the old green car. There is a confrontation, not only with the killer, but also with conscience for Kate and her married lover; she is able to discover her own strength without need of a fantasy life.

In Estelle Thompson's Hunter in the Dark (Walker, $7.95), a blind man, waiting at a bus stop, is chatting with a school girl when he hears a car pull to the curb and a man's voice offer a ride to Linda, using the girl's a field, and Philip Blair, a young school teacher blinded two years earlier, begins his search for a killer who had contemptuously dismissed him as a harmless witness.

It's a first-rate suspense tale with a surprising plot turn that has nothing to do with child molestation.

E. X. Ferrars is one of the reliable professionals in the field. Her latest, Last Will and Testament (Double-day Crime Club, $7.95), offers a gathering of assorted relatives who find that an autocratic old lady has left precious little spoils to divide. Her natural death, from a stroke, is followed by an unnatural death. This is not Ferrars at her best, but there is a likeable heroine with a charming cad of an ex-husband.