FOR A MAN who, Nikita Khruschev once said, would sit on a cake of ice on command, Soviet Foreign Minister Gromyko gave a very uncool performance in Moscow on Thursday. Obviously, he felt under heavy pressure to counter the substantial appeal of the American disarmament proposals to international opinion and to the Soviet public, which hears of them on foreign radio broadcasts. It led him to abandon the Soviets' usual reserve in strategic matters and, instead, to follow Jimmy Carter's example of going public. We don't find that alarming at all. On the contrary, it indicates Russian recognition that SALT touches issues of deep and legitimate concern to everybody. The American position, we are confident, can meet the test of public exposure and debate.

Mr. Gromyko complained that the Carter administration "crosses out all that has been achieved before" - by which he meant that Mr. Carter has cancelled the 1974 Vladivostok accord on offensive-missile ceilings. Surely he knows better. Vladivostok is still on the table. The hitch is that the Kremlin claims Vladivostok included cruise missiles, which incorporate the American technology the Russians are most eager to limit. But Mr. Carter declares, and Mr. Ford and Mr. Kissinger agree, that Vladivostok did not cover cruise missiles (or Backfire bombers). Was the negotiation sloppy? Anyway, things have changed.

"What has changed since Vladivostok?" Mr. Gromyko indignantly asked. An easy question, Andrei Andreyevich. Jimmy Carter is the President. Moscow wasn't ready for him, and it's stalling for time. Secretary Vance presented in Moscow a sweeping set of proposals for deep cuts and qualitative restraits in strategic arms. Negotiated out to mutual advantage, these proposals would, we believe, add stability to the Soviet-American strategic relationship. allow some diversion of resources from swords to plowshares and, non incidentally, enhance the ability of both great powers to press the cause of nuclear nonproliferation upon other countries. The Soviet military, political and bureaucratic elements identified with the programs the United States wants to limit evidentlly are not prepared to yield, if they finally do yield, without an argument. Mr. Gromyko was speaking for them in claiming that Mr. Carter seeks "unilateral advantage." He was if you will, negotiating.

Mr. Gromyko was careful to note, however, that "this does not mean that there are insurmountable obstacles." He issued not an ultimatum but an appeal for a "more realistic" American position. Mr. Vance, far for m saying take it or leave it, had only said that the American proposals "provide a reasonable basis for further discussions." Talks are to resume in Geneva in May. We think it is far too early to conclude that further negotiation cannot be productive, notwithstanding the unprofessional attack of the blues in which the Vance party indulged itself semi-publicly on the way home - such a display can only undercut the American negotiating position. Indeed, Mr. Gromyko suggested that, since Washington had made new proposals, Moscow might, too; he mentioned, among other items, American bases in Europe.

Mr. Carter has the initiative, and he has broad public and international support. He has as well, to judge by Mr. Gromyko's defensive explanations to the Russian people, some measure of Russian support. Soviet diplomacy may be limited by the apparently budding succession crisis provoked by Leonid Brezhnev's visibly failing health. But Mr. Carter is on a good wicket. We are pleased to see that he intends to stick on it.