Two computer companies announced plans yesterday to sell supercomputers made by other manufacturers.

The agreement will make it easier for American companies to sell such supercomputers to the Japanese Government and public universities in Japan, trade officials from both nations said.

Agreements have been reached on importing American beef and citrus, trading stock, practicing law, and selling semiconductors and supercomputers.

In 1991, Meiko sold supercomputers to an Israeli educational institution that was reportedly involved with the design of nuclear weapons.

But selling supercomputers to Russia - or even giving Russia's nuclear weapon scientists access to them - is still highly unlikely, Administration officials said.

Firms that sell supercomputers spend huge amounts on research and development and other fixed costs.

The Administration turned down applications last year from I.B.M. and Hewlett-Packard to sell supercomputers to Russia.

That led the American company, which was then a unit of Silicon Graphics, to file a complaint that Japanese companies were selling supercomputers below cost.

It was the first time that a Japanese company had tried to sell supercomputers directly to the United States Government.

The issue of continued Israeli and South African missile cooperation comes to the fore when the United States is considering selling supercomputers to Israel.