This book comes at a propitious time. Knee-deep in the Jimmy Carter era, insistent questions are being asked about his presidency and his powers.

Maeva Marcus does not answer those questions. She succeeds, however, in setting forth an excellent historical account of how a former president tried to cope with a threatened steel strike in 1952. In so doing, she delineates some of the limitations of any chief executive's power.

President Truman relied on "inherent" executive powers to justify seizure of the steel mills. But that the Supreme Court would not brook. In the steel case, the majority of the justices simply did not believe that the Korean war was an emergency as dire as painted by the president. So they invalidated the seizure.

Massively documented - there are 110 pages of notes and bibliography - the book is weaker when Marcus assesses the case's constitutional significance. She reads too much into it, ending by asserting that it "reaffirmed the basic principle of the rule of law and its corollary that the President, like every other citizen, is subject to the law." That at best is a half-truth, in spite of Richard Nixon's 1974 loss over the White House tapes.

Presidents are constrained more by politics than "the law." Law is much too fluid and uncertain to interdict presidents (and other high governmental officers). As Washington lawyer Charles Horsky once said, ours is emphatically a government of men and not of laws.

Those concerned about presidential power, as all should be, will profit from Marcus's historical account. The pity is that the book does not live up to its subtitle. (Columbia University, $14.95)