NEW YORK, JUNE 10 -- The Manhattan U.S. Attorney today made public written plea bargain agreements involving three prominent executives convicted in the Wall Street insider trading scandal.

The agreements, which lay out guilty pleas and terms of cooperation with the government, had been requested by members of the media.

Two of the agreements were released in their entirety -- one signed by former merger specialist Martin A. Siegel, the other by former brokerage executive Boyd L. Jefferies. Both men have already pleaded guilty to securities law violations.

But prosecutors withheld portions of a third agreement, which describes the terms of a deal struck last fall between the government and former stock speculator Ivan F. Boesky.

Assistant U.S. Attorney Charles M. Carberry, who is supervising a federal grand jury investigation arising from Boesky's cooperation, said in a letter to U.S. District Judge Morris Lasker that portions had been withheld because "release of some material in the agreement at this time would hinder ongoing criminal investigations."

Lasker has jurisdiction over the Boesky and Jefferies cases and will sentence the two former executives later this year.

One part of the agreement withheld by prosecutors was its date. However, a code on the Justice Department stationery on which the letter agreement was typed appeared to indicate a date of Sept. 18, 1986. Boesky is known to have finalized his cooperation with prosecutors sometime in September.

Boesky's plea bargain was disclosed on Nov. 14. He agreed to plead guilty to a single criminal charge and to forfeit $100 million to the government -- the largest insider trading settlement on record.

The date Boesky began cooperating with prosecutors is important because people familiar with the government's investigation have said that Boesky secretly taped conversations last fall with a number of his Wall Street colleagues. The government has never confirmed that Boesky began to cooperate with prosecutors as early as September.

People familiar with the investigation have said that negotiations are continuing over the tapes Boesky made last fall.

Boesky has provided evidence about possible securities law violations involving several prominent Wall Street figures, according to people familiar with the government's probe. Included in that was evidence about Drexel Burnham Lambert Inc. executive Michael Milken, corporate raider Victor Posner and TWA Chairman Carl Icahn, the sources said. Boesky also led government prosecutors to Jefferies and Siegel.

Siegel's plea agreement showed that the former Kidder, Peabody & Co. merger specialist began his formal cooperation with prosecutors on Dec. 23, 1986 -- six weeks before information Siegel provided led prosecutors to arrest three prominent Wall Street executives.

The third agreement disclosed that if Boyd Jefferies, who formerly headed the Jefferies & Co. brokerage, abides by the terms of his deal with prosecutors, neither the Jefferies firm nor any of its employes will be prosecuted for "their actions undertaken at Mr. Jefferies' direction or with his approval."