The Kremlin's old guard, already dwindled by death, has begun to be edged out by Soviet leader Mikhail Gorbachev, who is now showing greater impatience to put his own people in power.

Yesterday's retirement of Premier Nikolai Tikhonov, 80, was perhaps the clearest signal so far that Gorbachev, 54, is entering a new stage in his campaign to shake up and rejuvenate the Soviet bureaucracy. Tikhonov's job was to oversee the vast apparatus of ministries that, in the view of some Soviet analysts, are the centers of resistance to Gorbachev's proposals for economic revitalization.

By replacing Tikhonov with Nikolai Ryzhkov, 24 years his junior and a man with considerable economic experience, Gorbachev is giving the ministries notice that he intends to have his program put into effect energetically and without delay.

Although no one expects the premier's job to regain the foreign policy and ideological functions it once had under Alexei Kosygin, it is likely to grow in stature under Ryzhkov, if only because he becomes the executor of Gorbachev's domestic program.

Some western diplomats here took the unusual timing of Tikhonov's retirement as a sign that Gorbachev's push for economic changes may already have run into resistance, forcing the change at the top of the Soviet government to come sooner rather than later. Typically, they say, such an announcement would have been made at a full session of the Supreme Soviet, or parliament, after a plenum of the Communist Party Central Committee.

The announcement came the same week that the ruling Politburo took up a series of documents and programs crucial to the Gorbachev reign -- including a draft proposal on the 1986-90 five-year plan, the party program and revised party rules to be adopted at the 27th Communist Party congress next February.

Information on the draft five-year plan has been tightly held, particularly since last June when Gorbachev publicly said that the plan would have to be revised.

Some western diplomats speculated that difficulties over the plan may have come up recently, prompting Gorbachev to move quickly with the appointment of his close ally Ryzhkov so as to keep closer tabs on the plan's reception snd progress.

Others noted that the replacement of Tikhonov took place upon the return from vacation of Egor Ligachev, who now unofficially holds the second-ranking position in the party.

Ligachev, like Ryzhkov, has made a meteoric rise, starting under the late Soviet leader Yuri Andropov. Both Ryzhkov and Ligachev lived much of their lives outside European Russia, backgrounds that reflect a shift in the Soviet center of power out toward the military-industrial complexes of the Urals and mineral-rich Siberia.

Ligachev is now considered to hold the portfolio for ideology and is in charge of personnel, a critical and powerful job in the preparations for the party congress.

While Ryzhkov can be expected to prod the government and its ministries to follow Gorbachev's lead, Ligachev has been doing the preliminary work among party officials. Since January, when many believe Gorbachev first began to exercise his authority, 32 of the party's first secretaries have been replaced, compared with seven in the first 10 months of the late Konstantin Chernenko's reign.

The relatively rapid rate of change among the nation's 157 republic and regional party bosses has sent a message through the system, warning an older generation of leaders either to change their attitudes or make way for a younger group.

Gorbachev seems to have made certain that the example has been set at the highest level of government. Andrei Gromyko, 76, was replaced as foreign minister by Eduard Shevardnadze, 57, and now Tikhonov, the Politburo's oldest member, by its second youngest.

Yesterday's announcement was carefully staged to show that Tikhonov was leaving in good graces. Many believe that the health reasons given for his retirement are probably true given his age, although he did make an appearance this week at a reception for Hungarian leader Janos Kadar.

In the case of Politburo member Grigori Romanov, Gorbachev showed his ability to move swiftly and harshly against political opponents. Romanov, the former party boss of Leningrad, was ousted from the Politburo in July and has since plummeted from sight.

There is persistent speculation that Politburo member Viktor Grishin, the Moscow party chief, may also be on his way out sometime before the party congress.

Gorbachev's heavy domestic agenda in the next few months, starting with the drafting of the party program, the five-year plan and culminating in the party congress next February, is often cited as an opportunity for him to make changes -- in personnel and policy -- early in his tenure. But it also puts pressure on him to act fast, to consolidate his position before his opponents can recoup their strength.