A visitor to the White House walked unescorted and unannounced into Jimmy Carter's study on Friday and asked the President for direction to the office of an aide, White House sources said.

According to the sources, the President told the young man he was uncertain of the location of the aide's office, but believed it to be downstairs.

The Secret Service said yesterday that it was investigating the incident, but that information received thus far indicates that the visitor, whose name was withheld, did not enter Mr. Carter's study.

"Our information is that he did not enter any of the offices occupied by the President," said Jack Warner, spokesman for the Secret Service, which is in charge of protecting the President.

Warner added that the visitor, who was interviewed by the Secret Service, had an appointment at the White House, had been cleared to enter at the Northwest gate, and "was carrying the proper visitor pass credentials."

The spokesman said that the Secret Service is reviving the matter to determine whether any breach of security was involved in the visit.

According to White House sources, the visitor had an appointment with Mark A. Siegel, an aide to presidential assistant Hamilton Jordan.

Siegel was reported yesterday to be on vacation and unreachable by telephone.

The White House press office referred inquiries about the alleged incident to the Secret Service.

A well-placed source in the White House, said the incident involving the visitor was a topic of discussion there Friday.

As the incident was recounted, the source said, the visitor entered the west wing, and "somehow managed to go out along the veranda and into the Oval Office . . ."

From there, according to the accounts, the man entered Carter's study, "encountered the President and asked the President where Mark Siegel's office was.