CLEAR AND STRONG, a trumpet sings out above the back-up instruments as the song opens. The rhythm seems familiar enough-just can't quite place it. Someone turns up the volume on the radio as guesses about the song fly about the car. With the first word sung, everyone knows the answer but looks no less puzzled because, well, that's Bob Dylan singing, and what the hell is he doing with a trumpet player and three smooth-singing female background vocalists in his group?

The song "Is Your Love In Vain" and the rest of Dylan's recently released Street Legal album rekindle the cries that he has sold out and, worse, sold out to pop. The critics-confident they finally have the smoking gun-begin once again to close in on Dylan; but as the trial opens the only one missing from the scene is the Jack of Hearts himself. Dylan, it seems, has slipped away by declaring himself an "entertainer" and by developing a style to prove it; he shrugs off criticism as if those who simply view him as a poet-prophet gone bad are holding up a ghost for judgment.

Something happened over the last few years, the last few months. When we last remember leaving Dylan, it was amid no little confusion. History and myth, past hits and hints at new styles were tangled up in the touring Rolling Thunder Revue, the film Renaldo and Clara and the albums Desire and Hard Rain. Dylan was on shaky ground and knew it. The best moments of the period-the Revue and the concert footage in Renaldo and Clara-were a bow to the past, finding little support in Dylan's more recent work. The Revue, above all, indicated that it was time for Dylan to be moving on if he wanted to recapture the balance between old songs and new styles he had used so effectively years before.

Perhaps it is time to take a look at Dylan-as-Entertainer, as the charges of sell-out begin to ring more and more trite, if no less true; now more than any time in the past few years Dylan is trying out a new style both on the road and in the studio. After seeing Neil Diamond play Las Vegas, Dylan turned his attention to making his own concerts more "entertaining," even going so far as to hire Diamond's manager. Perhaps that explains the liner photo chosen for Street Legal-a shot of Dylan in a white suit holding the microphone and casting a challenging look to the audience, with the guitar that he hid behind for so many years nowhere in sight.

Street Legal is Dylan's most ambitious album since Blood on the Tracks. Carefully matching vocals with instrumentals and relying heavily on three female background vocalists, Dylan has his new style coming through on every cut. While the songs are linked together by a common style and, to a lesser degree, common lyrical themes, they are far from consistent and stand together almost as an ad hoc collection of musical experiments, with Dylan the Mixer finding still more ways to work background vocals into his songs.

"Is Your Love in Vain?" is the most popular song on the album-and the most mediocre. The trumpet-heralded introduction sounds smooth, all right, but the pastiche of instrumentals, background vocals and Dylan's lyrics fails to gel. The instrumentals and female vocalists in the chorus only serve to take away what power the lyrics have; in addition, the words themselves are not above suspicion, with lines like "All right, I'll take a chance, I'll fall in love with you" and the chorus "Are you going to risk it all, or is your love in vain?" Smooth, but it's all been done before and been done better.

On "Where Are You Tonight," the "new" Dylan strikes his most attractive pose. The song captures that wild feeling of America at night, the America of Thomas Wolfe and Jack Kerouac. The lean background vocals, snappy rhythm and fine lyrics about two-bit criminals and their women ("Her father emphasized, you got to be more than street-wise") work together to make "Where Are You Tonight?" perhaps the most polished song Dylan has written since Tangled up in Blue.

In "No Time To Think" Dylan is up to his old tricks, making lengthy alliterative lists of words and then complaining (mocking?) that there's no time to think. The short, repetitive rhythm matches the lyrics well and the sparring use of background singers livens up what might otherwise be an oppressively boring song.

DYLAN TRIES TO FIT a ballad into his new style in "Changin of the Guard", but cannot quite pull it off. The ballad's lyrics, full of the never-quite-clear symbols Dylan has used with such relish over the past few years, just does not mesh with the music; the keyboard work is a little too slick, the background vocals too pat.

When things just weren't clicking, Dylan used to rely on his rasping voice to carry him through the more strained lines-and it frequently worked. As instrumentals and background vocals become more predominant in Dylan's work, however, he can no longer side-step lines with a snarl. For example, the bouncy style of "True Love Tends To Forget" gives him no way to sing the lines "I saw you drift into infinity and come back again" without sounding stupid. In the worst songs of the album-"True Love," "We Better Talk This Over" and "New Pony"-the lyrics fall flat, while the instrumentals and heavy back-up vocals in the choruses compound the injury by making the tunes well-night indistinguishable from a thousand pop-rock songs.

As Dylan's lyrics return to the more personal tone of Blood on the Tracks and he places more emphasis on the tools of pop-rock, we see that Dylan has been down this way before, striving to develop a new style. Those who have not already written him off for billing himself as an entertainer can only hope that in future albums Dylan will be more discriminating.