WASHINGTON -- Federal law-enforcement officers are investigating whether Russell E. Weston Jr. first sought to attack the White House on Friday morning before shifting his focus to the Capitol, officials said Monday.

In fact, Lewis C. Merletti, the Director of the Secret Service, believes that Weston was "casing" the White House for a possible attempt on President Clinton's life that day, one Secret Service official said.

Investigators are trying to determine whether Weston was deterred from attacking the White House by its formidable security, leading him to turn his attention away from Clinton, who had been a recurring subject of what the authorities describe as his delusional rantings over the years.

Investigators said that they were still piecing together Weston's movements in the hours before his attack on the Capitol but that they had now talked to several witnesses who said they believed they saw him in Lafayette Park near the White House on Friday morning.

Among them is John M. Broder, White House correspondent of The New York Times, who was interviewed by the Secret Service on Saturday after informing the agency that a man matching Weston's description talked to him in Lafayette Park about 9:45 A.M. on Friday.

Broder identified the 41-year-old Weston from photographs shown him by the head of the Washington field office of the Secret Service and two other Secret Service agents.

In reconstructing his conversation with Weston, Broder said he was sitting on a bench in Lafayette Park when Weston approached and began to speak to him, warning that "the storm clouds of war" were gathering over Washington. Weston, Broder said, then gestured toward the White House and added that millions would die "because of the people you put in that house."

Weston was intense and his speech incoherent, Broder said, and he was carrying a small bag similar to an army ammunition satchel. But he did not make any specific threats against Clinton or any other Federal official.

Weston's presence near the White House on Friday morning would suggest that he went there as soon as he arrived in Washington from his hometown, Valmeyer, Ill., which, his family has said, he left late Thursday morning.

It is about 750 miles from there to Washington, which would have given him little time for any stops, particularly since he was traveling in his old Chevrolet pickup.

In any case, officials said they were still conducting a detailed investigation of his route.

The witnesses who believe they saw Weston in Lafayette Park, combined with his frequent remarks about Clinton, have convinced the Secret Service that he came to Washington with the President on his mind.

Paranoid schizophrenia was diagnosed more than a decade ago in Weston, who suffers from delusions and was briefly institutionalized in a Montana mental hospital in 1996. Earlier that year he was interviewed twice by the Secret Service, which had been alerted by local law-enforcement officials because of comments he had made about the President. The Secret Service arranged for him to be examined by a mental health professional, but at the time he was deemed unlikely to commit violence.

Then, in July 1996, about three months before he was involuntarily committed to the mental hospital, Weston drove up to the front security gate of the Central Intelligence Agency's headquarters in Langley, Va., and said he had information to report. He proceeded to harangue the agency's security guards for two hours. In that confrontation and in later letters to the C.I.A., one as recent as this May, he said that he and Clinton were clones, that Clinton was responsible for the assassination of President John F. Kennedy and that he himself was a brigadier general who had invented a time-travel machine. Weston also sent the agency a job application.

Given the evidence suggesting his insanity, some Federal investigators caution that it will be difficult to determine whether Weston had any clear motives or a focused target when he arrived in Washington. Indeed, while investigators look into whether Clinton was his chief target, some officials say they may never know what drove him to violence. They note that Weston, still hospitalized, has not yet been interviewed by investigators, and so they have not heard his version of events.

"Maybe," one official said, "he doesn't even know what his motive was."