Maybe it was the ghost of Richard Nixon at work. Or maybe it was just sheer coincidence, as the Air Force says.

Whatever it was, reporters who had covered the opening ceremonies for the Nixon library were surprised to discover in the early morning hours Saturday, when returning from a three-day trip with President Bush, that they could not get off Andrews Air Force Base without going through a sobriety checkpoint.

Air Force One and the White House press plane take off from and return to Andrews after presidential trips. Some reporters are known to have an occasional drink en route home from trips, particularly when the flight home is a four-hour one, as it was Friday, and the day's work is done.

As journalists were leaving the Andrews press center to head for their cars early Saturday, they were informed that sobriety checkpoints had been set up on the roads out of the airbase. Each car was stopped by an officer who stuck his head in the window and asked questions such as whether the driver had been drinking on the press plane. It was unclear, and Andrews officials would not answer, whether anyone was actually asked to walk a straight line or take a breath test. Several reporters said they were given literature on the dangers of drinking and driving.

White House officials are effectively immune to such procedures. They have limousines or vans to ferry them to and from Andrews and rarely are forced to drive their cars. Officials who were asked whether the White House had suggested, asked for, or arranged such tests said they were flabbergasted at any suggestion they knew of or sought the tests.

An Andrews spokesman, Sgt. Dale Warman, said that it was the first time such sobriety checks had occurred on an evening a White House trip was concluding at Andrews. But he said that was "purely coincidental" and added that no journalist or White House official had been charged with any violation as a result of the checks.