In assembly-line fashion, about two dozen Republican senators or candidates for the Senate filed through the Oval Office yesterday to be filmed and photographed with President Bush in anticipation of the fall campaign.

Acting White House political director David A. Carney arranged the sessions, which began with a gathering in the Cabinet room with White House Chief of Staff John H. Sununu and other officials. The candidates got to talk about substantive concerns while waiting for their individual meetings with Bush.

Those sessions, lasting two to five minutes, should provide plenty of footage for use in campaign TV spots. When one Republican candidate was finished, officials said, another was ushered in. Carney said Bush knew virtually everyone in the group, so their conversations were "relaxed and informal. . . . This was not a script-kind of an operation."

When the individual meet-and-greet sessions were concluded, Bush then filmed 27 individual endorsements, each one crafted for the candidate and citing specific home-state concerns. The Republican National Committee paid for the film crews and costs and the candidates will pay for airing the ads.

President Ronald Reagan made similar endorsement ads but GOP officials could not recall an operation as methodical as this one, or a prior administration willing to devote the time and effort to personalizing all the messages. Bush's willingness, one official said, "is a function of the fact that he was a party chairman once and a vice president, and you can't underestimate that."