The White House, trying to blunt recent campaign questions about President Reagan's health, yesterday released a new statement from a doctor who examined him in May, describing him as "a mentally alert, robust man who appears younger than his stated age."

The statement came in response to questions from reporters this week about the 73-year-old president's performance in Sunday's debate with Democratic presidential nominee Walter F. Mondale.

Meanwhile, Mondale's physician of 20 years, Dr. Milton M. Hurwitz of St. Paul, Minn., said in an interview yesterday that Mondale, 56, is in "excellent health . . . . As far as I know, he has no health problems other than high blood pressure, which is very well controlled."

Mondale has taken medication since 1971 to keep his blood pressure in the normal range.

The medical information released on Reagan yesterday was a more detailed report of a physical examination that Reagan underwent on May 18 at the National Naval Medical Center in Bethesda. At that time, the White House statement from Navy Capt. W.W. Karney, the internist who supervised the exam, said "the president is in very exceptional physical condition."

The May statement made no reference to Reagan's mental status. White House spokesman Larry Speakes said yesterday that the entire statement had been in Karney's full report to Reagan's doctor, Daniel Ruge. "I just picked up a partial quote in May," he said.

The May statement said the results of Reagan's physical were "entirely normal." Yesterday's release included additional figures to support this.

An outside physician, Dr. Thomas A. Pearson of Johns Hopkins Hospital, said that, "in terms of laboratory values, he appears to be an example of what we aim for in preventive programs and that is a person in the eighth decade of life who appears to be in excellent functional condition. Who could ask for more?"

Pearson added, however, that in general the risk of getting such chronic conditions as heart disease and cancer, as well as mental changes, can increase with age.

Reagan's blood pressure, at 140 over 80, was normal for a person his age, Pearson said, and his pulse of 72 "excellent."

Though the May statement did not refer to Reagan's hearing problem, yesterday's noted that his hearing in his right ear was "diminished." He wears a hearing aid.

Mondale's doctor said that the nominee takes three drugs daily to control his blood pressure and that at his last check in July it was 138 over 86, which is "indeed normal."

Although the drugs can sometimes produce side effects, including mood changes, Hurwitz said he and Mondale "have watched carefully for any evidence of any mood alteration and did not find any."