Mobil, in its unrestrained and feverish lusting after Marathon Oil, may have unwittingly done the impossible for its principal rival in that chase, U.S. Steel. Thanks to Mobil's public excesses, U.S. Steel, possibly for the first time in its corporate lifetime, has been widely viewed as an American underdog. That constitutes the major revamping of established perceptions and prejudices, which don't usually die easy.

But for recent mass revamping of a popular perception, Mobil runs a distant second to what the Reagan White House folks did while they were undoing Richard Allen as national security adviser. Less than seven weeks ago, Allen was the "heavy" whose reluctance to hurt foreigners' feelings had required his taking 1,000 American dollars from a few Japanese journalists who briefly interviewed Nancy Reagan. That was right after the inauguration. Before the inauguration, there had been the two Seiko quartz watches; later there would be a third. Yet, by political ineptitude and personal insensitivity, Allen's administration foes, by Jan. 4, had made him into a sympathetic underdog and managed to cast the president as a most unfeeling boss.

New Year's weekend was the worst. While the president was photographed with the secretary of state in Palm Springs meetings, the press was told that Allen was a goner and that his replacement, Deputy Secretary of State and Reagan intimate William Clark, was already on board. Nobody apparently bothered to tell Richard Allen or his little daughter, Kim, who accompanied her daddy when he spoke to the reporters outside their Virginia home.

On Monday, Allen, with all investigations of him officially terminated, reportedly had to push hard to get a personal meeting with Ronald Reagan. That's not at all consistent with the open Reagan style, so much admired.

But throughout the entire seven weeks, the White House handled matters badly. Facts and charges dribbled out. The soundest political approach in such cases as Allen's is to issue one statement incorporating the facts that are known and then to say no more until the investigation is completed. The Reagan people did just exactly the opposite, thereby fueling suspicions and, with responses to inquiries and frequent leaks, keeping the story on or near page one.

Ed Meese, the president's counselor and Allen's longest and strongest supporter inside, observed as early as Nov. 29 that "saying nothing probably would have been a better way of handling the whole matter." At that same time, Meese could manage a quip about the possible benefit of the Allen story's pushing budget director David Stockman, then recently incapacitated by an Atlantic undertow, off the front pages. "They've finally uncovered our well-laid game plan," said Meese.

That may have been the only semi- good line out of the entire Allen sacking. There were no winners, and Dick Allen was almost surely not the biggest loser. Neither Ronald Reagan nor most of his closest people came through this sorry episode as especially likable or admirable sorts. And for a president whom voters like personally more than they do his policies, that's not good.