Lengthy private talks here yesterday between Soviet leader Leonid Brezhnev and West German Chancellor Helmut Schmidt centered on disarmament but yielded no signs of progress and apparently included a Soviet refusal to trade any of its military superiority in Europe for a U.S. ban on neutron weapons.

After the second day for a four-day West German-Soviet summit, spokesmen for both sides indicated little progress was made on questions dealing with Berlin which the Germans view as a key measure of Soviet good will.

There were also some West German words of caution with respect to trends in trade between the two European powers, a subject that is of interest to the Kremlin.

Yesterday's talks lasted two-and-a-half hours, twice as long as the first day, and West German spokesmen described them as "a real dialogue." This was in contrast to what was, for Brezhnev and his hosts, a strange opening day on Thursday.

Thursday, West German sources said, the 71-year-old Soviet leader used up the entire scheduled one-hour meeting with Schmidt by reading a lengthy prepared statement. The chancellor had to extend the meeting 15 minutes to get in a reply.

There is great interest here in Brezhev's ailing health, and repeatedly arms and hands of Soviet aides or German hosts have reached out to steady him or help him.

After a photograph showing him being helped to his feet from a chair was widely reproduced, Brezhnev shooed away photographers yesterday telling an aide, "We can do without them."

During the day however, he seemed to recapture his more jovial gestures and there was no indication that the lengthy discussions were too much for him.

Although both leaders have stressed the great improvement in Soviet-West German relations in recent years and have generally attempted to create a good atmosphere for these talks the differences, especially on disarmament, are emerging publicly and there is no sign of any change in positions.

In a luncheon address, Schmidt stressed what are both West German and NATO concerns about the disparity in Warsaw Pact military strength arrayed against the West in terms of both ground armies and intermediaterange missiles targeted on Western Europe. A balance of forces is necessary for political-military stability, he said.

Schmidt expressed the hope that a new U.S.-Soviet strategic arms limitations agreement would be forthcoming soon and that this would lead to reductions in armies and in intermediate-range missiles at the East-West troop reduction talks in Vienna.

At a news briefing following the private talks however, Soviet spokesman Leonid Zamyatin indicated that the Kremlin was not prepared to allow the United States or NATO to use the neutron bomb as a bargaining chip in either the SALT or troop reductions forums.

Asked specifically about the issue, Zamyatin stressed that the neutron weapons was "clearly a weapon of mass destruction" and therefore should be banned internationally under a resolution covering such weapons which the Soviets will propose at the special U.N. session on disarmament later this month.

President Carter has announced a deferral of the decision to produce these weapons, which are meant to counter the vast numerical superiority of Soviet tank forces in Europe. The president said he would make his decision dependent upon Soviet attitudes toward arms control, stressing that a mere Soviet refusal to produce these weapons would not be sufficient.

The White Houe seems to want Soviet restraint, in particular, in deployment of the nuclear-tipped SS-20 intermediate-range missiles that worry Schmidt and the rest of Western Europe.

Both the neutron weapons and the SS-20 missiles are considered to be in the so-called "gray area" of weaponry that doesn't fall neatly into either the strategic arms, or troop reduction, talks.So some negotiating possibilities may still exist.

Brezhnev, in an interview published just before he arrived here, also talked of a willingness to cut ground troops by as much as 50 percent, provided the cuts left the current balance of forces undisturbed.

That proposal is being dismissed here as propaganda because the Western allies want the Soviets to withdraw some of their much larger tank armies from Eastern Europe in return for some U.S. nuclear weapon withdrawals in order to reach a common troop ceiling between opposing forces.

Schmidt is said to be probing the Soviet position to see if there is more give in it.

Today, the two leaders will sign the most positive step coming out of these talks, a new 25-year "framework" for economic cooperation.

But Bonn's economic spokesman said yesterday that in trade talks also going on here, the West Germans had expressed some concern about the increasing Soviet tendency to demand that Bonn accept repayment in so-called compensatory or barter deals.