MOSCOW, NOV. 23 -- It has been 21 years since Vladimir Kislik worked on plutonium production for the Soviet Union's atomic energy program. According to the 52-year-old scientist, everything he knew back then was long ago published in textbooks and is considered quaint and out of date by today's students.

But for the past 14 years, the "state secrets" Kislik learned in his job in the Ural mountains have been used to block his exit from the Soviet Union.

In 1973, he and his wife divorced, and she and his son left for Israel. Since then, as a result of his campaign for Jewish emigration, he has spent three weeks in a psychiatric hospital and three years in a labor camp and has no exit visa.

Tonight, Kislik played host to more than 100 people who jammed into his small Moscow apartment to listen to an unusual symposium entitled, "Refusal of permission to emigrate from the Soviet Union on grounds of state security."

The three-day symposium, which on Tuesday will split into three groups to discuss the legal and humanitarian aspects of the problem, addresses what is again becoming a key issue in the Soviet emigration movement. As the numbers of Soviet Jews allowed to emigrate begins to mount slowly again -- the total for 1987 is now about 6,000, six times greater than in all of 1986 -- attention is focused on the reasons that continue to hold back veteran refuseniks, those whose exit visas have repeatedly been denied.

There is no reliable estimate of the number of people denied exit visas on security grounds, but some refuseniks put the number in the hundreds.

Some of the most famous of those once blocked because of their knowledge of "state secrets" have recently been given permission to go, including Vladimir Slepak, Ida Nudel and Josef Begun. However, Naum Meiman, 76, who stopped work in the Soviet atomic program 32 years ago, has still had no word on an exit visa, even though his case was appealed to Soviet leader Mikhail Gorbachev in a letter signed by 100 members of the U.S. Senate.

A new commission attached to the presidium of the Supreme Soviet, the national legislature, reportedly is working to resolve appeals on security cases and according to one report, visas for 100 people have been granted over the last six months as a result.

But the commission's work is still regarded with suspicion by many long-time refuseniks. "The high authorities want to give permission to famous persons and that is all," Kislik said tonight.

At present, the term of "state secrets" is set by individual ministries and institutes according to unpublished guidelines. Spouses and family members are sometimes denied exit visas on the basis of relatives' past work. Men have sometimes been declared security risks because they served in the Soviet Army.

"The only thing secret about state secrets is how they decide to make them secret," said one long-time refusenik.

The three lead speakers at the opening session of the symposium illustrated the point: Pavel Abramovitch, an engineer, left his "security" job 17 years ago; Tsilya Reitburd, a geologist, and her husband, Emil Mendegeritsky, a technology professor, did "security" work 14 and nine years ago respectively.

The symposium is an attempt to elucidate a situation that organizers say is "characterized by arbitrary decision and extremely long, in fact indefinitely long, terms of refusals."

The speakers called for a procedure to rationalize what is a "collision of interests of the state and the individual," and to establish a maximum term for expiration of security clearance.

Now, visa applicants are often given no reason for their rejections and no fixed term for the duration of their "secrets," the group complained. "For many years their lives are suspended in the air and they face complete uncertainy as to their fate," one member said.

Recent press conferences have been called by refuseniks to focus attention on Soviet rules that require applicants for exit visas to get permission from parents or children who might have financial claims against them. This so-called "poor relative" rule is sometimes invoked by family members who do not want relatives to leave.