TO FIRE YOUR veteran foreign minister precisely as you announce your first summit?

This is what Mikhail Gorbachev did last Tuesday, with scarcely concealed disdain, to Andrei Gromyko, Stalin's wartime ambassador to Washington and later Soviet foreign minister for 28 years.

The Soviet Communist Party leader relieved the world's most experienced high-level diplomatist of his line position, kicking him upstairs with faint praise (his policy contribution was described as "considerable") to become head of state -- a chair he will presumably keep warm for himself. He replaced him with the former party leader and top cop of a small province, Georgian Eduard Shevardnadze, who, though he is no doubt a tough operator and an organization man in the Gorbachev mold, appears to have about as much familiarity with foreign affairs as he does with brain surgery.

It is a bold step for a new party chief, someone with only modest experience in security affairs, to oust the old pro of Soviet diplomacy and to replace him with someone substantially less well prepared than himself. Certainly it is a striking signal of Mr. Gorbachev's self-confidence and of the consolidation of his personal power. Here it counts that a day earlier he had removed from the party's inner circle an evident key rival, Grigori Romanov.

Beyond that, the move announces the assertiveness of a new leadership generation and an intent to establish not just tight control over a crucial policy area but also the dominance of party generalists of the Gorbachev-Shevardnadze sort over specialists (and empire builders?) such as Mr. Gromyko. Evidently this is how Mr. Gorbachev intends to get Russia moving again.

The meaning for the United States is something else. The Soviets who chat up American correspondents in Moscow have let it be known that Mr. Gromyko's ostensible promotion is actually something of a purge for having tried and failed to carry off accommodation with the United States.

Layers of this formulation are not easy to peel away. It appears, however, that at a time when the Soviet leadership has chosen to focus on domestic regeneration, it is advertising the outlines of a hard and steady foreign policy. Such a policy may emerge from the Kremlin's own political context; it is being justified in part by allusions to Ronald Reagan's hardness. It does not rule out agreements or selected reductions of tension with the United States, but it professes not to count on these developments and in any event, it seeks to put upon Washington the burden of opening the way.

Mr. Reagan and Mr. Gorbachev are to meet in Geneva in November. At the moment the two are in a stance of limited expectations but these things have a way of taking on a shape of their own as the event nears. Mr. Reagan is coming off a spell of heavy weather. Mr. Gorbachev is on a political roll. It is a time less of striking initiatives than of close and crucial calculation on both sides.