The Soviet Union, after 15 years of preparation, today published a new constitution that underscores the dominant role of the Communist Party, restricts free expression and apparently clears the way for party leader Leonid Brezhnev to become head of state.

None of these formulations or changes in ideological rhetoric - such as dropping "dictatorship of the proletariat" in favor of "state of the whole people" - will have any fundamental impact on the conduct of Soviet life or political policies.

The adjustments are essentially a refurbishing of party doctrine and the fact that they took so long to make shows how complicated debates on such matters can be in the Kremlin.

The new constitution, which has 173 articles, is to be formally adopted, after a "national debate," at a meeting of the Supreme Soviet next fall. It will replace a charter drawn up in 1936 by Joseph Stalin that Nikita Khrushchev first undertook to overhaul in 1962 as part of the de-stalinization process.

The only revision of immediate consequence appears to be in the makeup of the Presidium of the Supreme Soviet. It has been widely speculated since the ouster of Soviet President Nikolai Podgorny from the party Politburo last month that Brezhnev would shortly take his place as the ceremonial chief of state.

Such a shift would give Brezhnev equal protocol status with other Eastern European party leaders and his principal Western counterparts such as President Carter or French President Valery Giscard d-Estaing. The change would be purely symbolic since Brezhnev has already functioned for several years as the country's undisputed top man.

The new constitution adds a first vice president to the Presidium, which indicates that the person filling that post will assume the routine functions of a chief of state, such as receiving new ambassadors. Brezhnev, therefore, could have the additional title and grandeur without extra burdens.

It seems likely that the change would come after the new constitution is approved but it could also come on an interim basis as early as the spring meeting of the Supreme Soviet later this month, in time for Brezhnev's visit to France for talks with Giscard.

Western analysts now believe that Podgorny probably lost his Politburo job because he resisted making way for Brezhnev to be president. The issue may even have held up completion of the constitution for a time while Brezhnev and his allies maneuvered Podgorny out.

On the role of the Communist Party the new constitution is more explicit than the Stalin one, declaring that "th Communist Party of the Soviet Union is the leading and guiding force of Soviet society and the nucleus of its political system, of all state and public organizations. The Communist Party of the Soviet Union exists for the people and serves the people."

The old charter merely noted that the most "active and politically-conscious citizens" would be in the party, "which is the vanguard of the working people . . . both public and state."

As did its predecessor, the new constitution guarantees a wide range of freedoms: Speech, demonstration, worship, "privacy of correspondence, telephone conversations and telegraphic messages," among others. It is the systematic violation of those freedoms that forms the basis of most dissident protests about repression here.

To deal with such complaints, the charter sets out strict terms: "Exercise by citizens of rights and freedoms must not injure the interest of society and the state and the rights of other citizens." The documents also asserts that "exercise of rights and freedoms shall be inseparable from the performance by citizens of their duties."

In other words, the Kremlin has provided itself with a rationale - "the interests of society and the state" - for keeping the exercise of expression under tight control.

On provision of the old constitution that was retained comes as something of a surprise: The nominal right of individual Soviet republics such as the Ukraine, Armenia or the Baltic states to secede. That issue was considered one of the most contentious ones in the drafting of the document.

While referring to a single "Soviet people" and the "drawing together" of all nationalities in the country, the document stops short of eliminating the automony of the 14 republics which with the Russian federation make up the USSR. This too is basically a symbolic matter since the only real authority is in Moscow.

The demise of the "dictatorship of the proletariat" is in keeping with what Brezhnev called the "maturity" of the state in a speech presenting the constitution to the party Central Committee two weeks ago. Theoretically, classes have been abolished in the Soviet Union os that the dictatorship of one group over another no longer applies.

When the French Communist party dropped the hallowed term from its standard last year, the Kremlin was angered no by the edeological divergence, but because the French move represented a break with the Soviet have ackowledged that advocacy of "dictatorship" is outdated.

A new section of foreign policy has been included which reflects Moscow's well-known positions: "Supporting the struggle of peoples for national liberation . . . preventing wars of aggression . . . and consistently implementing the principle of peaceful coexistence." In the Soviet Union, the constitution declares, "war propaganda shall be prohibited by law."