Some months ago, Massachusetts Institute of Technology asked the federal government for permission to publish the results of an experiment using laser light to produce the isotope of uranium that generates nuclear energy.

The government refused. The Los Alamos Scientific Laboratory in New Mexico told MIT that publication would violate national security. Los Alamos said its scientists had conducted similar experiments in secret and felt that publication of the test results could lead a foreign power to use laser light to generate enough of the isotope uranium-235, to start an arsenal of atomic weapons.

The incident, which one Los Alamos scientist refers to as a "mutual editing agreement," spotlights a growing difference between scientists outside the federal government and inside it over what should be kept secret in the burgeoning new fields of laser enrichment and laser fusion.

One issue is the use of laser light to separate the isotopes of uranium to enrich the metal with enough fissile uranium to produce nuclear fuel or atomic bombs. A second issue involves the use of laser light to heat deuterium and tritium fuel to such high temperatures that they reach the heat of fusion that can theoretically supply the world with limitless energy.

"Parts of these two technologies are classified and will remain classified because they have applications to nuclear weapons," declares Frank Press. "This administration does not want to encourage access to nuclear weapons."

To many scientists at universities and in private industry, the tightening secrecy around laser enrichment and laser fusion represents little more than censorship. Both fields have undergone rapid and impressive advances the past five years; both fields are at the forefront of research that could lead to new sources of energy in the next 20 years.

"We don't agree with the classification process in laser fusion," said Dr. Moshe Lubin, director of the University of Rochester's Laser Energetics Laboratory. "We want a free discussion of ideas, we want some compromise by the government's national laboratories in this field."

At present, most of the exotic research in laser fusion in done at the Department of Energy's Lawrence Livermore Laboratory in California and at Los Alamos. Close behind is the University of Rochester, which has put together a consortium of institutions like the University of Michigan and private concerns like Standard Oil Co. of Ohio to pursue laser fusion research.

Rochester's laser has produced a pulse of almost two trillion watts which for a fraction of a second generated fuel temperatures of 67 million degrees.

The difference between Rochester and Livermore is in the power of their lasers and the size of their budgets. Rochester feels it cannot compete with Livermore, which often shoots its laser to study thermonuclear weapon effects. That's one reason Livermore classifies a lot of its laser fusion work.

The other reason is the design of the fuel pellets, or "targets" as they're known. No bigger than grains of salts, the fuel pellets are made of layers of glass that hold deuterium and tritium fuel in a way that will allow the fuel to heat up to temperatures of 100 million degrees. The same pellets are used as thermonuclear fuel in hydrogen bombs.

Secrecy is tighter surrounding the use of the laser in separating uranium isotopes. Most of the secret enrichment work is done at Los Alamos. Among the many private institutions pursuing laser enrichment are MIT, Battelle Research Institute and a joint subsidiary of Exxon and Avco.

The isotope of uranium known as U-235 (the fissile isotope used in nuclear fuel and atomic bombs) was first separated out of the natural uranium with laser light at Los Alamos in 1976. The way it was done is still secret, but it involved a laser whose light can be turned to frequencies that will cause isotopes of uranium to absorb laser light in a different way.

Whatever the method, laser enrichment promises rich rewards. Potentially, uranium can be enriched with lasers at 2 percent of the cost it's enriched at today. This is why so many private institutions want to research it and why the federal government wants to keep it so secret.

The key to the success of laser enrichment in 1976 was in getting a gas called uranium hexafluoride to remain a gas in a supercold state even colder than liquid air. Ironically, the United States kept that a secret until the Soviet Union disclosed all the details of its research on the matter in 1977. s

The censorship of the MIT experiment duplicating the Los Alamos work was not an isolated incident. Los Alamos scientists admit they've censored at, least 10 other outside experiments, usually those involving the frequencies of laser light that are best used to separate uranium isotopes from each other.

Where will it all end? University and industry scientists are itchy to move ahead with laser enrichment. The federal government is just as anixous to keep every advance a secret. Said one Los Alamos scientist who asked not to be identified: "The rules of secrecy we're working under right now will be here for many years to come."