WASHINGTON - The 25th Amendment to the Constitution sets out rules for the president to transfer his power to the vice president in case the president is unable to fulfill the duties of the office.

The amendment, approved in 1967, four years after President Kennedy was assassinated, provides for the temporary or permanent transfer of presidential power. It also allows the vice president and Congress to strip the president of power if he is unable to do the job.

Until it was added, the Constitution did not provide for what to do if a president was alive but unable to serve.

The amendment permits the vice president, when backed by a majority of the Cabinet, to assume presidential powers when he declares to the speaker of the House and the president pro tem of the Senate that the chief executive "is unable to discharge the duties and the powers of his office."

The amendment permits the president to resume those powers with a similar declaration, subject to a challenge by the vice president supported by a majority of the Cabinet.

The amendment sets out a 21-day period in which Congress, by two-thirds votes, would decide disputes.

President Clinton and Vice President Al Gore had a plan that would set in motion invocation of the 25th Amendment, but it was kept secret.

The first such plan was made in the 1980s by the first President Bush and Vice President Dan Quayle. Bush, who as Ronald Reagan's vice president saw the complications of a medical emergency firsthand, wanted strict succession rules laid out.

Medical and history experts contended that essentially no one was in charge of the country while a bullet was removed from the lung of a gravely injured Reagan after a 1981 assassination attempt.

Also, Reagan only nominally transferred power to Bush for several hours while he underwent colon cancer surgery in 1985.