THE TROUBLE with calling the Soviet Union the "focus of evil," as President Reagan did earlier this year, is not that the statement is demonstrably and totally false: there is some truth in it. Nor is it that such a statement offends Soviet sensibilities: the folks in the Kremlin are not all that delicate. The trouble is that to the extent Americans take the statement seriously, it removes the basis on which even a limited accommodation with the Soviet Union can be sought. How, after all, can one justify dealing with the devil? How can one justify not fighting the devil tooth and nail? This is the rhetorical hole in which Mr. Reagan's more extreme statements have deposited American foreign policy.

Now comes Secretary of State Shultz to take American policy out of that hole in a long statement lent added authority by having been personally cleared by the president, reporters were assured.

It is a no-nonsense, conservative statement; it is not a strident or abusive one. It disappoints those members of the Senate Foreign Relations Committee who are troubled generally by the administration's policy. But in characterizing the Soviet Union as a country open to a degree of gradual internal change and capable now of some restraint in its pursuit of self-interest, the statement brings American policy back into the intellectual mainstream.

"Strength and realism can deter war," Mr. Shultz declared, "but only direct dialogue and negotiation can open the path toward lasting peace." If that strikes you as unexceptionable, then compare it with the theory that intrigued the White House at the beginning of the Reagan administration: that the flexing of American military and economic power would compel the Soviet Union to come to American terms. Mr. Shultz now speaks as though the administration, having devoted its first two years-plus to restoring American strength, is ready for serious negotiation. Who outside the unreconstructed right would want to quibble with this formulation? Let the administration show it means what Mr. Shultz says.