Arnold Wesker's play "The Merchant," having its premiere at the Eisenhower through Nov. 5, is provocative and stimulating and should be one of New York's most arresting offerings of the theatrical season.

Inspired by an Olivier performance of "The Merchant of Venice," Wesker went back to some of Shakespeare's sources, as well as to modern studies of the 16th century, to come up with contemporary insights on that restless period. There is nothing sacred about plays and stories, Shakespeare himself rifled hundreds.

Of the three major successful with two. He imagines a strong friendship between Shylock and Antonio, the Christina from whom he is to cut his pound of flesh. Wesker lavishes as much love on Portia as did Shakespeare, adding contemporary light on her self-aware intelligence. Adjuring the romantic poetry, he has been far less successful with the Lorenzo-Jessica story.

While this play stands on its own, inevitably one discusses it in terms of its elder. Instead of serving as an incident affecting several young lovers, the Shylock story here dominates them.

This Shylock lives in a bustling home managed by his sister, with visitors in and out, a refugee committee, a tutor, portrait painter, his partner, a wholly different atmosphere from the earlier Shylock's shuttered home. Shylock has two loves, daughter Jessica, whom he takes for granted, and his books, which he takes for stimulus. Knowledge, not money, is his passion and sharing it with him is a Christian merchant from the ruling classes, stifled by trade and exhilarated by Shylock's zest for the paradoxes of history.

The Christian is Antonio, transformed from the earlier play, whose need for quick money to help a fawning godson prompts the bond for a pound of his flesh. Antonio insists that the bond be made because the laws of Venice demand such. He wants to protect his friend Shylock. In a spirit of mockery, Shylock proposes the terms. As a Jew, living with the curfews and strictures of the ghetto, Shylock expresses his disgust of hypocrisies by this bitter joke, a pound of flesh.

By giving Shylock outgoing bonhommie , family friends, knowledge and humor, Wesker creates a character of timeless appeal. The bond will cause Shylock to smile at "scholars who have more learning than wisdom."

Wesker's Portia, who must accept the Bessanio who solves the problem of gold, silver or lead, uses her insights even more clearly than does Shakespeare's heroine. Her resolution of the bond alerts her to Bassanio as an unreliable life partner but she will manage to make him think that her strength is his.

The Lorenzo-Jessica pairing works better in theory than practice. Instead of Shakespeare's withdrawn, foolish child. Wesker's Jessica is a further comment on the modern woman, but unlike Portia, Jessica, partly a spoiled brat, has been damaged by the ghetto. Her excuse for leaving her father is not valid in these altered circumstances and she evidently steals none of his money. But how did she and Lorenzo meet? What does each see in the other? Why is Lorenzo presented in a key of stiff artificiality at variance with the naturalism tone?"

The point that he is dabbling dilletante is clear enough in his words without making him a flop. It is highly amusing to hear Shylock's great speech ("Hath not a Jew eyes? Hath not a Jew hands, organ, dimensions?" pouring from Lornezo. The irony is delicious, the style wrong.

So. The Merchant" is not a finished production. There are tendencies toward fussiness. Pointing cutting and precision are in order.

Within Jocelyn Herbert's beautiful unit set, requiring only one scene to set its conventions. John Dexter's staging generally flows well and there are some excellent players.

Joseph Leon, in the title part the late Zero Mostel was to have played, quite possibly serves the play as a play better than a superstar might, yielding balance. Leon uses the humor and logic Wesker has given Shylock with fine, often subdued effect. While one can easily imagine Mostel, that now is irrelevant, unfair to Wesker, Leon and Mostel.

John Clements is a marvel of mellow assurance as Antonio, perfect casting. Glorious is the word for Roberta Maxwell's prescient Portia, a lovely actress with Jessica Tandy clarity. Marland Seldes rises to her major scene as the sister with that fine actress's command. There are other considered details in the visually rich production and it's good to see a large company (21) instead of our small, economy-sized casts.

But the play's the thing and "The Merchant" has the quality of a rich, considered statement by an original, inquiring mind.