Former stock speculator Ivan F. Boesky has led the government to "dozens" of securities industry professionals who remain under investigation in the continuing Wall Street stock trading scandal, according to a sentencing memo released by prosecutors yesterday.

The government said that more charges are expected, but it did not identify its targets in the 25-page sentencing memo, which contained large blanked-out sections to conceal material now before a grand jury.

Boesky will face a maximum of five years in prison when he is sentenced Friday on charges of violating securities laws. The extent of his cooperation with investigators is key to his hopes for leniency.

"Boesky indirectly and directly ... revealed that criminal conduct is at the heart of {a} substantial amount of market activity by established securities industry professionals," the government memo said. " ... Not since the legislative hearings leading to the passage of the 1933 and 1934 Securities Acts has the government learned so much at one time about securities law violations."

A memo on Boesky's behalf, prepared by his lawyers, also has been submitted to Judge Morris Lasker, who will impose the sentence. This document describes in some detail Boesky's efforts to secretly tape record conversations with his Wall Street contacts.

"An Assistant U.S. Attorney requested him to make and tape record telephone calls and to arrange and tape record meetings with other persons as directed by government investigators," the memo said. " ... Although fearful for his safety, he complied with the government's requests. He placed taped telephone calls and wore a body wire {microphone} to meetings with other persons at the direction of government agents.

" ... At that point in the investigation, government agents were sufficiently concerned by the possibility of retaliation to offer him physical protection... . It is difficult to get sophisticated professionals in the securities business to discuss and corroborate their past wrongful acts without arousing suspicions... . In each case, he successfully completed the assignment."

As has been previously reported, the government launched an investigation of the Drexel Burnham Lambert Inc. investment firm and the firm's Beverly Hills junk bond expert, Michael Milken, as a result of Boesky's cooperation. Drexel repeatedly has denied wrongdoing. While the Drexel probe is believed to be the most important continuing investigation, it was clear from altered portions of the documents released yesterday that information provided by Boesky has prompted investigators to pursue other leads.

"Boesky entered into unlawful agreements with others in order to trade in securities on the basis of inside information and to avoid certain regulatory restrictions on his brokerage business," the government memo said. "In addition, he agreed to accommodate others by purchasing or holding stock positions at their request; although Boesky seldom was told the purpose of those accommodations, his activities allowed others to achieve market-related advantages in securities transactions or to avoid regulatory restrictions."

Boesky, who settled SEC charges that he traded stocks on the basis of confidential information about corporate takeovers by paying the government $100 million in November 1986, led government investigators to former Wall Street dealmaker Martin A. Siegel, former brokerage chief Boyd L. Jefferies and numerous takeover financiers in Great Britain who were nabbed in connection with a scheme to seize control of Guinness PLC.

"Jefferies has confirmed Boesky's revelation of criminal accommodations for valued customers, a practice that apparently is deeply rooted in the brokerage industry," the government memo said.

Boesky's lawyers argue that he should receive a more lenient sentence than imprisoned former investment banker Dennis Levine, who led the government to Boesky. Levine, who is serving a two-year prison sentence, cooperated less extensively than Boesky and initially fought against the government's charges.

The memo submitted by the Manhattan office of U.S. Attorney Rudolph W. Giuliani urges Lasker to consider both the extensive nature of Boesky's crimes and his "outstanding" cooperation. Lasker has received numerous letters in support of Boesky including those from theater producer Joseph Papp, Claude Lannzmann (author and producer of the Shoah documentary about the Holocaust) and members of Boesky's immediate family.

"He has been isolated and emotionally incarcerated throughout the fifteen months he has spent cooperating," the defense memo said.