President Carter has dismantled most of three years' foreign policy accumulation in reaction to the Soviet invasion of Afghanistan, but a private intercession by a recent White House guest pointed up his problem: he is using the architects of the discredited old policies to shape drastically different new designs.

The intercession, clearly heard by more than a score of former high officials of past administrations invited to the White House on Jan. 8, came from James R. Schlesinger. Schlesinger has special credentials as an expert in national secruity and cabinet member under Nixon, Ford and Carter.

When Secretary of State Cyrus Vance told the former high officials that the Soviet invasion was "a test" of whether "the international community" could muster the strength and fortitude to prevent such Soviet conduct, Schlesinger rose and said, in effect: Cy, that's not the test. Its the leadership of this nation that's being tested.

Schlesinger's intercession obliquely addressed a question being heard as the new foreign policies forced on Jimmy Carter become visible: can the same principals who sponsored and carried out the now discarded and flawed policies of the first three Carter years switch in midstream and look good on a reverse course? This is not a case of changing horses in midstream but of changing streams without changing horses.

Four other guests of Carter voiced agrement with Schlesinger: John J. McCloy, the establishment Republican who goes back to Harry Truman's and Dwight Eisenhower's administrations; Donald Rumsfeld, defense secretary under Jerry Ford; Joseph J. Sisco, longtime State Department Mideast expert; Prof. Sam Huntington of Harvard, close friend of national security adviser Zbigniew Brzezinski.

That many of the most cherished policies Carter brought to the White House have been jettisoned, at least for now, is spectacularly clear. The long effort to discourage arms sales to Third World nations is down the drain, flushed there by Pakistan's dire need; the policy of refusing all arms to states suspected of building nuclear weapons has met the same fate for the same reason; so has the president's sometimes self-defeating emphasis on human rights.

Closer to home is the president's decision ("We told him again and again it just had to be done," said one White House aide) to shelve his most important issue of the first term: the strategic arms limitation agreement (SALT II). That installs the despised Kissingerian "linkage" as high policy. Also gone are early hopes for major reduction in military spending and top priority on courtship of the Third World.

Yet officials responsible for carrying out all the old policies remain in place. A symbolic case in point is the new head of Voice of America, Mary Bitterman. She was named only weeks before the Soviet invasion of Afghanistan elevated the VOA to new importance as the carrier of news about Carter's toughened foreign policy.

But Bitterman is an unlikely head of VOA to perform that new mission. Presidential aides say she was picked for only two reasons: her political clout in Hawaii, where she has headed public radio broadcasting, and her avid support of George McGovern in the 1972 presidential campaign.

The Bitterman decision symbolizes the striking changes in U.S. policy before and after Afghanistan. "She wouldn't have been considered for the job if the Soviets had made their move at the time," one official told us. "It was just a job then, but now it's one of Carter's most important."

The same is true of posts throughout Carter's national security bureaucracy essential to his success in carrying out his toughened new policies. But the president so far has shown no awareness that these new policies may need new principals to run them -- men and women not ideologically committed to a world that the Soviets have obliterated by taking over Afghanistan.

Many politicians of both parties, while applauding Carter's belated moves against Soviet expansion, believe the president's long lack of awareness is a portent of deep problems ahead. They worry that Carter himself, despite strong talk, has missed the full import of the Soviet invasion.

If he has not, they ask, what makes him stick to his old mentors? These were the very officials in control for the three years during which, by his own testimony, he was so completely misled by the Soviet Union.