The government's timid handling of the case against former CIA Director Richard M. Helms could undermine any effective oversight of the nation's intelligence community, according to a key member of the Senate Intelligence Committee.

Sen. Joseph R. Biden Jr. (D-Del.) said his apprehensions are supported by a secret and still incomplete study of espionage cases that his subcommittee on secrecy launched about a year ago. He said it has already turned up abundant evidence that what might be termed "legitimate blackmail" has taken place to preclude prosecution "in an astonishing number of cases."

Helms has faced a possible perjury indictment for his Senate testimony in 1973 about Central Intelligence Agency operations in Chile, but Justice Department prescutors have said they feared top-secret information might be disclosed if he were brought to trial. As a result, they initiated a round of plea-bargaining that ended with his pleading no contest to two misdemeanor charges for failing to testify "fully . . . and accurately."

The former CIA director was fined $2,000 and given a suspended sentence earlier this month. Despite a tongue-lashing by the judge, Helms and his lawyer both publicly described the conviction as "a badge of honor."

In remarks prepared for delivery at Bowdoin College in Maine last night, Biden said he intends to begin Senate hearings next month in search of a better solution.

He said he has never argued "for the 'drawing and quartering' of Richard Helm," but he is still "deeply disturbed with the possible precedent this case may set, and especially the process by which this decision was made."

Calling the Helms case "an obvious threat" to the admittedly imperfect arrangements for congressional oversight of the nation's intelligence agencies. Biden said:

"It could easily be misinterpreted to stand for the proposition that a member of the intelligence community could still come before our special intelligence committee and lie to our committee about activities which were in obvious violation of any arrangement we had established, or indeed, any charter that had been written by the committee."

Beyond that, Biden said, any criminal penalties that Congress might lay down for various prohibited activities would appear to be meaningless.

"Any official of the intelligence community could simply take the position that there was very sensitive national security information necessary to prove the case against him; he would insist upon its disclosure, (and) the government, not wanting to jeopardize the information, would drop the case," Biden said.

Biden said his subcommittee's study, undertaken last year, is still only half inished, but it has already established that "in many espionage cases the FBI will not even begin the investigation and the Justice Department rarely prosecutes because investigation or prosecution is fruitless."

"What seems to happen in these cases is that the defendant who has engaged in the most heinous form of espionage, who has taken the most sensitive of information has the greatest likelihood of enjoying immunity from prosecution."

The subcommittee chairman cited two other cases already on the public record of the national security syndrome at work. One involved a CIA operative named Puttsporn Khrankhruan who was indicted in 1973 as a member of a multi-million-dollar opium-smuggling ring, but was later released when the CIA refused to supply documents the prosecution needed.

The other was the original Watergate investigation, which was temperarily thwarted by White House-planted hints that top through an inquiry might endanger CIA operations in Mexico.

In each instance, as in the Helms case, Biden protested, "it appears the Department of Justice was pressured, if not coeroed, by claims of national security to back away from very inportant criminal investigations or prosecutions. This is a process which we cannot permit to continue."

The senator said one solution might be secret, or in camera, court inspection of supposedly sensitive materials such as U.S. District Court Judge John J. Sirica's review of President Nixon's Watergate tapes recording. But in any event, Biden warned that "if we cannot fashion an acceptable solution . . . secrecy will have become a real cancer devouring our government. It will not only create an impasse in the administration of justice, paralyzing the Department of Justice, but it will ultimately destroy whatever little credibility we have been able to restore in our government in recent months."