Soviet President Leonid Brezhnev, in a surprising statement to 12 U.S. senators last night at the Kremlin, disclosed that the Soviet Union "tested" its own nuetron bomb "many years ago . . . but never started production."

The Soviets have maintained throughout a long, bitter propaganda attack on the United States' own enhanced radiation weapon that the Russians could build one themselves, but had rejected it on humanitarian grounds.

The 71-year-old leaders' brief description of the Soviet test of the controversial nuclear device is contained in a detailed "memorandum of conversation" released by the senators. Brezhnev made the comments to the Americans during a 70-minute meeting in his office. The Soviet news agency Tass in reporting Brezhnev's remarks, made no mention of his "neutron bomb" disclosure.

"There is lots of talk about the neutron bomb," Brezhnev is quoted as saying in the senators' memorandum. "Many years ago, our tester, Korolyov, tested that bomb. No, it was academician Korolyov, the physicist. In his day he tested that. We tested but we never started production of that weapon."

Western military experts said the Soviets may have tested a low-yield nuclear device in which radiation effects exceed the blast and heat yiedls. This could be termed a "neutron bomb."

The United States is considering production of a neutron weapon - a deployment of neutron artillery shells exceptionally effective in crippling a massive tank assault without destroying urban centers. U.S. experts expressed doubts that the Russians have the technology required to miniaturize a neutron device for use in a 155-mm artillery shell.

Moreover, the neutron weapons do not have priority in Soviet strategic needs since the Russians enjoy an overwhelming advantage in terms of number of tanks deployed in Eastern Europe.

The Russians have campaigned against U.S. production of neutron weapons/mainly because their use would be politically more acceptable loan using tactical nuclear arms. The Russians would have little use for a low-yield "neutron bomb" in view of their overall defense strategy, according to these experts.

The memo, drawn up by an aide to Sen. Abraham Ribicoff (D-Conn), co-leader of the delegation, quotes Brezhnev as saying:

I often think why is it that the United States and the president take such (hostile) attitudes toward the Soviet Union. Have we done something bad toward the United States? No, we have put forth peace proposals. But in the United States, any excuse is used to criticize and to attack the Soviet Union.

I see it and I say go ahead, shout say whatever you will, you have your ideology. Carter and I know we both have a couple doren minutes when satellites will tell us missiles are coming. We will never be the first to let such weapons fly.I will still have time to respond. There will be no more United States.

"But we will still get it in the neck."

The memo provides a rare glimpse of an earthier, more direct Brezhnev than that cast in the official descriptions of his conversations or the guarded talks of Western diplomats who meet with him.

U.S. Ambassador Malcolm Toon had advised the senators not to talk with correspondents in detail of their meeting with Brezhnev.

Ribicoff said the meetings provided an "upbeat" ending to the three days of talks the senators have had with high-level Soviet officials. The talks chiefly have focused on the strategic arms limitation treaty now in the final stages of negotiation between the two superpowers.

Ribicoff said the delegation had been "chilled" by a stormy session Thursday with Premier Alexei Kosygin at which the Americans had pressed the point that Soviet actions on human rights, military involvement in Africa and the Mideast and other areas could adversely affect what is predicted to be a close vote to ratify the approaching SALT treaty.

The Americans said a genuine Soviet conviction for peace was coupled with insistence that the United States is responsible for tensions between the two countries.

Brezhnev hit both themes in his prepared remarks, which were translated while the senators and Ribicoff aide Arthur House took notes.

"Frankly, the present state of affairs does not satisfy us completely," Brezhnev said. "Lately there has been some approach from the perspective of realism - I see a need for building relations on the basis of equality, non-interference in each other's affairs and mututal benefit."

"Unfortunately, we see no way of cooling down those in the U.S. opposed to good relations. They are in favor of crossing out all good things achieved, they want to whip up an arms race, they have absurd concoctions about a so-called 'Soviet military threat.'"

Brezhnev added, "You have seen the losses of the Soviet people during the war. Twenty million were lost in defense of Soviet ideals. We have not labored to rebuild our century in order to have another war. All we do today and all our plans relate to grandiose and peaceful construction. We need no land because we have enough. We do not need to conquer the U.S. or Europe even if we could. We do not want to unleash a nuclear war because we are not crazy. What we want is lasting peace with all countries."

Saying the SALT II agreement is 95 percent ready, he said: "Who stands in the way?" Here on finds the line of those in the U.S. who want to frustrate those talks or who seek an outcome to the detriment of the Soviet Union. That we can never except.

"We are told the U.S. Congress will not approve an agreement it regards as bad. It is the Soviet Union, not the U.S. which would have to dismantle strategic arms to reach treaty ceilings. But we advocate a treaty nonetheless because we think it serves the goal fo mutual security."

Brezhnev asserted that when the "basis of respect, partnership and no attempts to interfere in internal affairs . . . was broken, our relations worsened and we moved to periods of tersions."

Remarking that he knew "in the U.S. generally and in the Senate in particular there are various views on U.S. Soviet relations," Brezhnev complained. "Sometimes I feel some abuse in their references." But he said he agreed with President Carter's assertion at the White House Thursday that tensions are lessening between Moscow and Washington.

"President Carter has expressed a desire to meet with me. I too would like to meet with him.But we should do it when we have a new agreement we could sign. If not, we could meet and talk and part. The venue is not important to me. We could meet any place . . . such as Washington or Moscow, but the substance of the agreement is important to me.

"Outer space allows us to see how many nuclear missiles are on both sides. It would suffice for one bomb to hit to have a thrid and nuclear was break out. And nothing would be left of our talks and all these papers . . . " At this point Brezhnev made his disclosure about the neutron bomb and discussed possible consequences of a nuclear war.