Soviet President Leonid Brezhnov flew to Prague today to attend Czechoslovak Communist Party congress and East Germany sent "fresh reserves" to join Warsaw Pact maneuvers around Poland.

Expectations here and in Prague that Brezhnev's unusual journey signaled a new East Block summit on the Polish crisis diminished when a senior Czechoslovak official said the other pact delegations to the congress would not be held by their party chiefs -- a departure from usual practice when Brezhnev makes a personal visit.

The delegation accompanying Brezhnev did not include any of the senior Politburo members, such as Defense Minister Dmitri Ustinov, KGB chief Yuri Andropov, or Premier Nikolai Tikonov, thereby reducing the impact of the Soviet president's presence in Prague.

Instead of a full-fledged pact session, it is now expected the Soviets will gather views from the other bloc countries as the Kremlin mulls what to do about the crisis that has brought economic chaos to Poland and strained Moscow's ties with that country's Communist Party.

The indications that there is not to be a summit Moscow interpreted by some here to mean Moscow is still willing to allow the Poles more time to work out their problems short of an intervention. The West has warned that such a move would have severe consequences for relations with the Soviets.

[In Washington, administration officials said President Reagan sent a message to Brezhnev on Poland, The Associated Press reported. They gave no details.]

ADN, the official East German news agency, said the newly dispatched units "from deep inside home territory" met with Soviet units "from next door" and pledged to "use all their strength to reliably defend socialists achievements and the peaceful life of the citizenry against all imperialist blows."

The Soyuz 81 military maneuvers are already the longest-running such exercises in the past 10 years.

"Covered by air defense forces, units of motor infantry, tanks missiles and artillery, as well as a reconnaissance, engineer and intelligence units were moved into designated areas by rail transport or in military columns," said ADN. "Other forces were brought to the coast by landing craft."

The report did not indicate how many new troops, or precisely when or where they are now stationed. But the descriptions said the units were receiving "poltical and military briefings on their forthcoming battle tasks," making clear the Soyuz, meaning "unity," excerise would go on.

Poland itself was quiet today and there were no indications of new labor difficulties of the kind that have prompted the Soviet press to warn Poland Publicly of a threat of counterrevolution and anti-Communist Party activities since the formation of Solidarity, the first independent trade union in Communist-ruled state.

In Warsaw, it was announced that Stefan Olszowski, widely regarded as the leading hard-liner in Poland's ruling Politburo, was leading the Polish delegation to Prague.

While Brezhnev is in Prague, Soviet Premier Tikhonov is scheduled to begin a five-day visit to Austria Monday and Foreign Minister Andrei Gromyko is to receive Hungary's foreign minister here this week in a routine meeting.

The atmosphere in Moscow remains tense and the situation extremely fluid. "It can change from day to day now," one foreign diplomat said," depending on the dynamics within Poland and the momentum within the Soviet leadership to resolve matters."

Although the Kremlin leadership has been silent on its own view of the situation, there is no doubt that momentum, as the Westerner said, is building. In the past decade, as Brezhnev's health declined and his power increased, he has not normally attended party gatherings in the six buffer states, sending other Politburo members in his place. He sat attended the Prague congress in 1971, a session that formally condemned as a "counterrevolution" the party crisis that triggered the last Soviet intervention in the bloc in 1968.

The official Tass news agency reported from Prague that Brezhnev and Czechoslovak leader Gustav Husak "had a conversation" at Hradcany Castle in which "they informed each other aobut topical questions" of a bilateral nature and "exchanged views on some international problems. The conversation was held in a cordial and fraternal atmosphere."

The Czechoslovak press has taken a hard line on the Polish crisis, reflecting both Husak's fealty to Moscow and the Prague leadership's concerns that the "Polish disease" has resonance within Czechoslovakia.

The intimidating tone of such dispatches as that from East Berlin today is seen by Westerners here as part of a deliberate intensification of the war of nerves against Poland over the past three weeks. Pravda added to this today. In a front-page editorial describing the Bulgarian party congress, which ended last week, the paper declared that "any deviation, even the slightest, from Marixism-Leninism and proletarian internationalism invariably has brought on grave consequences for socialism."

In addition, reflecting deep Kremlin ire at the failure of Polish party chief Stanislaw Kania to avoid fresh compromises with Solidarity in heading off a nationwide strike threat last week, Pravda asserted that "this is no longer a pressure on the government, but a direct struggle against the existing state system, against socialism."

Senior commentator Vsevolod Olchinnikov declared that the Polish party plenum last week that preceded the strike settlement had asserted, "It is possible to take the country out of the crisis only by stopping the dangerous trend toward converting Solidarity into a destructive political force, into an organization against the government."

It ssems increasingly clear here that Moscow wants Kania to crack down on the political activists of KOR, the Committee for Social Self-Defense, whom the Soviet have labeled "antisocialists" conspiring with "imperialists" in the United States and West Germany to undermine party authority. So far, Kania has not complied, but his actions in the next few days or weeks may determine his own future in power, if not the fate of country.