West German Chancellor Helmut Schmidt said today that he was unable in two days of difficult talks to convince Soviet President Leonid Brezhnev that the United States is serious in its intentions to negotiate reductions in medium-range nuclear weapons in Europe.

Schmidt, reporting to his Social Democratic Party's parliamentary group on his talks with Brezhnev, which ended today, said he was convinced of the "earnest will" of the Soviet Union to realize substantial cuts in its medium range weapon systems.

But despite his intense efforts during eight hours of talks with Brezhnev to portray President Reagan in a similar light, there was little sign of a change in Soviet attitudes or bargaining positions as Moscow and Washington near the opening next week of talks in Geneva on reducing European-based medium-range nuclear weapons.

"It is more than clear that the Soviet leadership cannot yet correctly assess the intentions of American leadership," Schmidt said.

The same assertion earlier in the day by his spokesman, Kurt Becker, was sharply disputed by Leonid Zamyatin, a senior Soviet official who serves as Brezhnev's spokesman. Zamyatin insisted that the Soviets had not misjudged what he called the militant aims of the Reagan administration.

"If the West German side has drawn such a conclusion from the talks," he told reporters, "then it is wrong in its assessment of the Soviet position toward the United States."

Recalling statements by the Reagan administration on the possible use of nuclear weapons, Zamyatin said it would be "an unpardonable mistake" to regard such talk as merely propaganda.

Zamyatin's consistently harsh performance before reporters here dramatically underscored the differences in Soviet and West German perception and policy -- differences Schmidt and Brezhnev, however, have given the impression of managing much more evenly.

Brezhnev is to leave for Moscow tomorrow morning and the two sides are expected then to issue a joint communique on the talks, the Soviet leader's first in a Western country since the Soviet Union invaded Afghanistan nearly two years ago.

In statements this evening after their final formal meeting, the two leaders acknowledged disagreements between them but stressed the value of their talks in furthering mutual understanding.

Anticipating claims that his talks with the Kremlin leader had failed to achieve any significant result for the West, Schmidt told his party colleagues that he had not expected that the Soviet Union would change its negotiating position or show any hint of compromise so close to the start of U.S.-Soviet negotiations. Nor, he said, had the Soviets expected him to represent anything other than the Western position.

"We have attempted to remove serious Soviet doubts about the credibility of the American position and about the U.S. leadership's serious readiness to negotiate," Schmidt said.

Describing his role as an "interpreter," Schmidt said he had not been able to allay Soviet worries about the planned stationing in West Germany and several other Western European countries of U.S. Pershing II and cruise missiles.

"On the contrary," he said, "I have stressed that their worries correspond to our own worries about growing Soviet rocket capacity that is pointed at Western Europe."

Schmidt said he had put Reagan's offer to the Soviets of a "zero solution" to the problem of nuclear medium-range systems in the "foreground" of the talks. Under this proposal, made by Reagan last week, the United States would cancel the scheduled initial deployment of the new missile in December 1983 if the Soviets would dismantle their new SS20 and old SS4 and SS5 medium-range nuclear missiles targeted against Western Europe and China.

Brezhnev yesterday rejected the proposal and renewed an offer of a mutual East-West moratorium on deployment of medium-range nuclear systems in Europe for the duration of the Geneva talks. As a sweetener to this offer and as a preliminary contribution to the Geneva negotiations, Brezhnev attached a second proposal -- also not a new one -- to reduce "a certain portion" of the Soviet systems now located in the European part of the Soviet Union.

While Schmnidt has been quick in the past to reject Soviet offers of a moratorium, Bonn was reluctant to rebut Brezhnev's latest proposal before studying it thoroughly.

But West German sources close to the talks described the new Soviet offer as apparently nothing more than a combination of elements that have already figured in the public discussion. Bonn spokesman Becker said today that Schmidt's basic attitude on the moratorium idea has not changed.

A moratorium is opposed by Western governments because it is seen as freezing the superiority of Soviet nuclear systems in Europe. Schmidt, referring today to Brezhnev's offer, noted that the Soviet superiority had increased since the last time Brezhnev visited Bonn in l978.

Then, the number of SS20 nuclear warheads was 150, Schmidt said, and today it tops 750.

But Zamyatin, in a comment that carried a veiled warning of a continued Soviet buildup, cited Western reports that an additional SS20 is deployed each week and noted that a year has passed since Moscow first presented its moratorium proposal.

Contrary to the Western claim that there is an imbalance of nuclear forces in Europe, the Soviets have consistently argued that an approximate parity prevails and that the new U.S. weapons would tip the balance.

In a recent interview in Der Spiegel magazine, Brezhnev claimed that the Soviets had 975 nuclear medium range launchers in Europe compared to 986 equivalent Western systems. Today, according to Zamyatin, Brezhnev broke down this figure in a memo to Schmidt as follows: 496 land-based medium-range rockets, 18 sea-based medium-range rockets, and 461 medium-range bombers.

The figures correspond roughly to estimates already published by the London-based Institute for Strategic Studies.

The only apparent area of common ground found here with regard to negoatiations was a willingness Brezhnev voiced to Schmnidt to approach the bargaining in stages.

But the Soviets remained vague on what they want included in the initial phase, according to a West German source. This issue promises to be among the major points of dispute in the negotiations.

The Reagan administration, backed by the European allies, wants to limit the first phase to land-based, medium-range missile systems in the hope that by focusing on a relatively narrow field of weapons, the chances of agreement will be better.

The Soviets have insisted that the negotiations also include the U.S. forward-based systems -- the nuclear-capable, medium-range aircraft assigned for use in Europe. Because the Soviets consider these systems a major threat, U.S. negotiators expect it will not be easy to have them set aside for a later stage of the talks.