WHEN Leonid Ilyich Brezhnev seized power in 1964, he seemed little more than an "apparatchik" who had mastered the levers of an Oriental political structure. As one who then stayed atop the slippery Soviet pole for 18 years, Mr. Brezhnev, who died Wednesday at age 75, surely qualified as a connoisseur of power.

Yet he developed an unmistakable political style of his own. Forsaking both Stalin's direct personal brutality and Khrushchev's rough-and-tumble, he built a working consensus among the dozen or so men who run the Soviet Union. For some years, he did this so well that an argument stirred in the West: was the Soviet Union still a compulsively ideological totalitarian state, one bent first on competing with the West, or was it becoming tentatively pluralistic and coexistence-minded, desiring first, or also, to improve life at home?

The Brezhnev answer became clearer through the 1970s. Arriving at personal authority just as his country arrived at full great-power status, Mr. Brezhnev could not resist testing the new opportunities for unilateral advantage that world disorder and American distraction strewed in the Soviet path. True, he did accept the inhibitions that nuclear survival places on superpower maneuver. But he conducted a foreign policy that in the end valued empire over d,etente in the American mode.

This two-dimensional man -- his most widely reported human quality was a taste for expensive Western cars -- had no uplifting vision of Soviet life. The one "doctrine" to which he lent his name rationalized aggression. From his 18 years of leadership, the Soviet citizenry profited only modestly. He left a host of Russia-sized problems: a foreshortened d,etente, an unreconciled China and a sullen Poland, an occupied and resisting Afghanistan, a dragging economy, a social structure under class, ethnic and generational stress, a hollow ideology -- and a continuing monopoly on power by a self-selected Communist elite.

The new leadership, likely representing in the first instance the consensus Mr. Brezhnev built, does not appear to offer the United States any immediate relief. But it may yet come to its own choices of world role and quality of life, and these may allow Americans a certain wedge of influence. The right message to get across is that the United States is prepared to be firm but accommodating. If there is to be a further bleakness in Soviet-American relations, it should not come about because the United States sent misleading signals or was unprepared to deal.