George Bush's commitment to keep a weakened Mikhail Gorbachev in power reached a troubling high point at their summit-closing press conference yesterday, when Bush allowed to stand uncorrected the Soviet president's powerful but fraudulent case for blocking Baltic independence.

Mixing lawyerly brilliance with political artistry, Gorbachev in effect threw the Baltics back at the U.S. president. He said that if an American state made the mistake of trying to secede, Bush "would have resolved this in 24 hours." That compares apples and oranges: a union forced by military takeover to a voluntary union of equals.

Bush's barely-heard response, "Well done, well done," matched his downgrading of all disagreements. The intense, dominating Russian had the offensive, extracting the trade agreement essential to him and eloquently selling his Baltic and German policies. However it plays in Moscow, the result here is unease among Bush advisers, who believe arm's length, not the embrace of a pal, is the only correct U.S. posture toward a Soviet leader.

At last December's Malta summit, Bush went beyond the course proposed by his advisers and set his companionship with Gorbachev on its present risky course of friendship. The true feelings of these aides spilled out when, assembled on the White House lawn awaiting the Soviet president last Wednesday, they exchanged negative comments about him.

Their attitude was well expressed by an informal counselor to the White House who, because he is not on the government payroll, can talk freely to the Soviets. ''Whether Gorbachev stays in power or doesn't,'' he told Yevgeny Primakov, a member of the President's Council, on Thursday, ''is none of our business. It's your business.'' Primakov responded with a small laugh.

Making Gorbachev's survival part of ''our business'' is dangerous because it skews Bush's negotiating positions. Although clear from the start that there would be no agreement on Germany or the Baltics, it can be questioned whether Bush's conciliatory reaction to Soviet demands expressed here was shaded by concern for his new friend.

More basic is the question of how valuable over the long run is a Soviet ''partner'' weak enough to require propping up by the United States. Such handling of Gorbachev suggests the ''clientitis'' syndrome that has raised strident criticism in the past of American protection for far lesser lights than Gorbachev: the Shah of Iran, Nguyen Van Thieu, Ferdinand Marcos.

Boris Yeltsin, the enemy of our friend, becomes an enemy of the United States. When the flamboyant Russian populist visited here last September, he was not invited to the Oval Office in a deliberate snub. He has been lately ridiculed in private at the White House and State Department as a ''buffoon'' and ''flaky.'' His election last week as president of the giant Russian Republic, claimed officials at State, cast a shadow over the summit.

Heaping ridicule on a possible successor to Gorbachev astonishes American specialists on Soviet affairs outside the administration and dismays key State Department policymakers. White House Chief of Staff John Sununu is no foreign policy expert, but he is an accomplished politician well-versed enough to treat Yeltsin with public respect after his election.

Not all Bush policymakers perceive Gorbachev as fondly as their chief and many key advisers. The Russian's transparent negotiating tactic of beseeching Americans for sympathy, while blustering with menace as the world's only other military superpower, is not enjoyed everywhere in the administration.

The Soviet president surely proved he can still evoke Gorbymania on the streets of Washington, but he has not cut quite the gallant figure so admired at past summits. During his two and one-half hour breakfast with congressional leaders Friday, he abjured the jousting with American lawmakers that seemed to please him before. ''I thought he was just less buoyant than in the past,'' House Armed Services Chairman Les Aspin told us.

Buoyancy suffers whenever a chief magistrate must endure political, economic and territorial disintegration. A Moscow poll, conducted by North Carolina's Independent Opinion Research and Communications in conjunction with the Soviet Academy of Sciences, was released here as Gorbachev hit town. It showed his approval rating by Muscovites down from 92 percent in 1988 to 78 percent in 1989 to 22 percent in 1990. George Bush can do nothing about that for "my pal," Mikhail.