When Rep. John M. Murphy (D-N.Y.) goes on trial for his Abscam involvement this month, you'll be reading excerpts from FBI videotapes which, the government claims, will prove that the congressman took a bribe. Murphy insists that the same videotapes will exonerate him of any wrongdoing.

Yesterday, I provided a preview of some damaging evidence -- a videotape showing Murphy instructing an associate, Howard L. Criden, to accept a briefcase stuffed with $50,000 in $100 bills.

Murphy has said he thought the briefcase contained immigration application forms for an Arab "sheik" whose representatives has asked for his help. The sheik's men were actually FBI agents and a convicted con artist, Mel Weinberg, who cooked up the Abscam "sting" operation.

My associate Gary Cohn has reviewed the videotapes, which were ordered sealed by a federal judge. In today's installment, a major element of the government's case is laid bare: "Criden, the unwitting middleman, and Laurence Buser, a longtime, trusted associate of Murphy, discuss with Weinberg and FBI agent Anthony Amoroso -- the "shiek's" men -- a lucrat lucrative business deal that is to be financed by the Arab and assured of success by Murphy's influence in Congress.

Unfortunately for government prosecutors, Murphy was not present at the meeting, held in a luxurious Washington town house. The government must prove that the deal was cooked up with Murphy's knowledge and approval, and that may not be easy.

Buser outlined the deal while the hidden cameras recorded it. The government of Puerto Rico, he explained, was trying to unload its shipping operation, the Puerto Rican Maritime Authority, to private buyers. Murphy, with his clout as chairman of the House Merchant Marine Committee, would arrange favorable purchase terms for the sheik -- and would be a secret part-owner of the new company.

If necessary, Buser promised, Murphy would see that legislation was passed to protect the company and ensure a fat return for everyone.

Weinberg interrupted the lengthy presentation and got down to the nitty-gritty: "Will he be a partner in this with us?"

Buser: "Well, he'll be a silent partner, I would imagine."

Criden chimed in, explaining that as head of the Merchant Marine Committee, Murphy "can't be anything else" but a silent partner.

Weinberg: "The main thing is, do you think that Murphy can make the deal?"

Buser: "Murphy can start the deal, I'll finish the deal."

The sheik's men expressed doubts that Murphy had the power to assure a profitable venture, and Buser was happy to reassure them.

Buser: "I don't know what you understand about American politics, but Murphy's power right now, as chairman of the Merchant Marine Committee -- whatever legislation goes up on the floor of the House, he is the manager of that legislation.

"He can take it in any direction he wants to take it, and control it . . . He's a past master . . . Right now, we're manipulating this [Omnibus Maritime] bill . . . Murphy and I see a potential . . . The thing is to mainipulate the acquisitions with the bill. So that you protect everything that . . . we can possibly get out of the government."

Weinberg: "So what you're telling me, we need Murphy. He's the key to behind the whole thing?"

Buser: "Without him, we could get screwed . . . Now we waited all this time, and we looked at a few companies . . . but we haven't made a move. Now he [Murphy] says to me, 'I think the time is right to make a move.' And I agree with him . . . I think we can do a deal."

During his trial, Murphy reportedly will argue that Buser lied when he told the undercover agents that he had Murphy's cooperation.

Footnote: The undercover agents met again with Buser to make the final arrangements for the shipping deal. This time, Murphy was present. But, the G-men couldn't wring any incriminating statements out of the congressman. I'll provide excerpts from that videotape in a future column.