President Reagan is wearing a hearing aid, White House officials said yesterday after the president was seen wearing what appeared to be a small one in his right ear at a White House ceremony.

Reagan began using the hearing aid last weekend, according to White House spokesman Larry Speakes, who said the 72-year-old president was advised to use the electronic device after his ears were examined in Los Angeles Aug. 22 and it was discovered that the hearing in his right ear had deteriorated.

"It was fitted when he visited with his specialist in California. . . and the doctor recommended it, it was prescribed, the president has it and he is wearing it," said Speakes, who would not say what percentage of the president's hearing has been lost.

Asked if the hearing aid indicated that the president's health may be failing because of his age, Speakes said: "What's age got to do with hearing?" Later he added that the president may forgo his annual physical this year because "the man is in such great shape."

In addition to the hearing aid the president wears contact lenses and glasses on occasion and suffers from a relatively rare hereditary illness called Dupetron's Contraction, which has caused a hard shell to grow around a tendon in his left hand, causing a finger to curl and become inflexible.

The president also disclosed in a recent interview that because of occasional lapses in his memory he has started to keep a diary to impress events on his mind.

The president has had trouble hearing questions and other conversation for several years. During the 1980 presidential campaign his aides discussed whether to have him wear a hearing aid, and decided against it because it would remind voters of the president's age. Speakes said yesterday that last month's recommendation by Dr. John House that Reagan wear a hearing aid was the first time a doctor had advised the president to use one.

According to Reagan the loss of hearing is due to an injury incurred during the filming of a movie in the late 1930s in which he played Secret Service agent Brass Bancroft and a gun was unintentionally fired near his ear.

Reagan was seen wearing the hearing aid yesterday at an East Room ceremony to mark the beginning of a national voluntary program to combat illiteracy. The government will offer an additional $310 million to organize college students to tutor the illiterate.

"Conservative estimates are that 23 million Americans . . . are functionally illiterate . . . , " the president said. "Let us resolve today to roll up our sleeves and get to work because there's very much to be done."

Meanwhile, White House officials said they doubt that White House chief of staff James A. Baker III will be hurt by a report that a former Reagan aide recalled making copies of Carter briefing material on four occasions for Baker. That account, reportedly given by the former aide to a House investigative panel, appears to raise questions about Baker's contention that he dealt only briefly with any Carter briefing material.

A White House aide described the reported account by Mark Ashworth, who was in charge of the duplicating machine at Reagan's campaign headquarters, as improbable. They described Ashworth as a "low-level errand boy," and said it was unlikely that anyone could remember specific documents among several thousand documents copied nearly four years ago.