Ronald Reagan is not the first president to undergo surgery or to suffer some major disabling condition that raises fears that the chief executive might be unable to carry out his duties.

In two cases, total disability lasted months. James A. Garfield lingered 80 days before dying in 1881 of an assassin's bullet. In more modern times, Woodrow Wilson suffered a stroke and was an invalid for the remaining 17 months of his presidency.

On Sept. 25, 1919, Wilson collapsed while on a nationwide speaking tour to support the League of Nations treaty. On Oct. 3, in the capital, he suffered a paralytic stroke. For months he left his bed only to exercise or engage in purely formal functions, and he sometimes was so weak than his wife reportedly had to guide his hand when signing documents.

He did not call a Cabinet meeting until April 13, 1920. And it is widely believed that for some time after his stroke, he was incapable of exercising the powers of office.

In Wilson's day, before the nuclear age and blanket press and television coverage, it was relatively easy to hide a debilitating condition. But today, the world knows within minutes that something has happened to the chief executive.

Since the beginning of World War II, two presidents -- John F. Kennedy and Franklin D. Roosevelt -- have died in office. Reagan himself was incapacitated by gunshots from a would-be assassin; Lyndon B. Johnson had a gallbladder operation, and Dwight D. Eisenhower had a heart attack, an intestinal operation and a stroke.

The Eisenhower experience led Congress in 1965 to approve a constitutional amendment, which became the 25th Amendment in 1967, providing for the vice president to become acting president whenever a president declared himself unable to carry out his duties or whenever the vice president and Cabinet declared the president unable to do so.

The first presidential disability since World War II started occurred April 12, 1945, when Roosevelt suffered a cerebral hemorrhage and died. Vice President Harry S Truman was sworn in that day.

Truman was described in 1949 by the White House physician, Brig. Gen. Wallace Graham, as virtually "an iron man." His only recorded illness in office was a mild virus infection from July 14 to 19, 1952.

Eisenhower suffered a heart attack Sept. 24, 1955, at 2:45 a.m.. He had played 27 holes of golf the previous day while vacationing in the Denver area.

For the next few days, there was talk that Vice President Richard M. Nixon might take over in an "actng" capacity with authority to be delegated by Eisenhower, but the constitutional situation was unclear.

Eisenhower, in Fitzsimons General Hospital near Denver, was in an oxygen tent for several days, but his wife, Mamie, reportedly was able to visit him Sept. 26 while he ate lunch with the tent removed.

Within a few days, talk of delegating presidential powers ended. On the basis of an examination Sept. 26 by a Boston heart specialist, Dr. Paul Dudley White, White House aides said the president could start reading documents and meeting with top officials in about two weeks.

By October, the president was carrying on business from his Army hospital suite. After recuperating at his Gettysburg, Pa., farm, he resumed "full duties" at the White House Jan. 9, 1956.

On June 9, 1956, Eisenhower had surgery at Walter Reed Army Medical Center for ileitis, a disorder of the small intestine. He walked out of Walter Reed on Mamie's arm the morning of June 30 and stayed at his farm until returning to the White House July 15. About a week later he went on what was described as a "strenuous" three-day tour of Panama. Although Democrats charged that his health problems were being covered up, he won reelection in a landslide.

On Nov. 25, 1957, Eisenhower suffered a mild stroke that affected his speech for a period. Initially, White House aides told the press that the president had suffered a "chill," but on Nov. 26 doctors revealed he had had an "occlusion of a small branch of a cerebral vessel which has produced a slight difficulty in speaking" but no other abnormalities.

He was back on the job in a few days, and his speech problem gradually disappeared.

Kennedy, the next president, suffered no severely disabling diseases or injuries while in office. But Nov. 22, 1963, in Dallas, he was shot by an assassin later identified by a presidential commission as Lee Harvey Oswald. Kennedy died in Parkland Memorial Hospital. Vice President Lyndon B. Johnson was sworn in as president 1 hour and 39 minutes later.

On Oct. 8, 1965, Johnson had surgery at Bethesda Naval Hospital for removal of his gallbladder and a kidney stone, but his doctors pronounced him able to make presidential decisions right after the operation. He soon went to his ranch in Texas for a recuperation period that ended Nov. 14.

A day after the operation, Johnson signed a bill doubling his administration's efforts in the War on Poverty, and on Oct. 20, he exuberantly displayed his abdominal scar to photographers in a famous bare-belly picture.

Just before going into the operating room, Johnson revealed that he and Vice President Hubert H. Humphrey had agreed that if Johnson were unable to carry out his duties, he would ask Humphrey to serve as acting president.

If he were unable to inform Humphrey of his incapacity, the vice president, after "such consultation as seems to him appropriate," would assume the role of acting president.

Johnson said similar agreements had been made by Eisenhower with Nixon and Kennedy with Johnson.

Thirteen months later, on Nov. 16, 1966, Johnson had a double operation at Bethesda that his doctors termed "minor." A polyp on his throat was removed and found to be benign, and a hernia near the scar of his gallbladder operation was repaired. On Nov. 19 he left the hospital and flew to his ranch for recuperation.

President Nixon suffered no seriously disabling physical conditions while in office, although on July 12, 1973, he was hospitalized at Bethesda for viral pneumonia. Nixon also suffered from phlebitis in his left leg, which was reported as serious in June 1974, just months before he resigned the presidency.

Phlebitis is an inflammation of the veins that hampers circulation. It can lead to blood-clotting and endanger life.

Gerald R. Ford, who succeeded Nixon, suffered only the aches of banged-up football knees from his days as a high-school and college star.

Jimmy Carter, Ford's successor, had painful chronic hemorrhoids, but they posed no serious difficulty in his job. Carter also broke his collarbone while skiing cross-country at Camp David on Dec. 27, 1980, but was able to walk back to his lodge.

A potentially more serious incident occurred Sept. 15, 1979. Carter, an avid runner, was participating in a 6.2-mile race in the hills near Camp David.

He was seen to wobble, moan and stagger; another racer said his face was "ashen," and Secret Servicemen running alongside grabbed his arms and aided him to a golf cart. A few hours later, after examination showed nothing wrong, he joined other runners at a picnic and said, "I feel great."

On March 30, 1981, Reagan was shot while leaving the Washington Hilton Hotel by John W. Hinckley Jr., now confined to St. Elizabeths Hospital.

The president was driven to George Washington University Hospital for three hours of emergency surgery to remove the bullet that entered under an armpit, struck a rib and burrowed into his left lung. He received a transfusion of 2 1/2 quarts of blood.

At 7:25 p.m., five hours after the shooting, he was out of surgery and in stable condition.

That day, there was considerable confusion as to who was in charge during the emergency. Then-Secretary of State Alexander M. Haig Jr., appearing in the White House briefing room at about 4 p.m., told reporters, "Constitutionally you have the president, the vice president and the secretary of state in that order . . . . As of now, I am in control here pending return of the vice president."

The speaker of the House actually is third in line of succession according to law.

Within a day, Reagan was making a remarkable recovery, reportedly in excellent spirits and cracking jokes with those attending him.