Veterans Affairs Secretary Edward J. Derwinski is not likely to soon forget listening to President Bush's State of the Union message last year -- Derwinski's first as a member of the Cabinet.

While his fellow Cabinet members sat in rapt attention in the House, Derwinski spent the evening in the basement of a Northern Virginia pizza parlor, watching the speech on a big-screen television set with a Secret Service detail and a few White House staff members.

Derwinski was, in his words, "the designated non-attendee."

In one of Washington's best-known but little-discussed secrets, one member of the Cabinet traditionally is asked not to attend the president's State of the Union message or other speeches to joint sessions of Congress. Fearful that some catastrophic event might kill the president and all 17 officials in the line of presidential succession, one Cabinet member is kept away to ensure there will be a president.

White House officials declined yesterday to give details of the practice, citing security concerns. "There will be one that stays home, but we never say which one it was," said press secretary Marlin Fitzwater.

Other officials sought to separate the policy from the massive amount of security that will surround the president's speech tonight, saying that the policy was not new and had nothing to do with terrorist fears growing out of the Persian Gulf War.

"It's just a tradition when you have that many individuals in one place with the opportunity for a mishap," explained deputy White House press secretary Stephen T. Hart.

"It's really rather routine, except for the awesome nature of it," said Derwinski.

What happens, according to Derwinski and others, is that several days before the speech, the secretary to the Cabinet, a White House officer, will notify a Cabinet member that he or she should plan not to attend the speech. If a Cabinet officer is traveling outside Washington, that person typically will be designated and given added security during the speech.

T.H. Bell, the Reagan administration's first education secretary, recalled in his autobiography how excited he was about hearing the State of the Union in person for the first time. Then the telephone rang in his government car as he was headed for Capitol Hill. It was then-White House Chief of Staff James A. Baker III with instructions.

"I got sent home," Bell recalled telling his wife as he entered their Arlington home. "But don't worry. Before this is over I might be the president of the United States."

Bell said Baker cited a law, supposedly directing that all the officials in the line of succession not be in the same place. White House officials said yesterday they know of no such law and described the policy as one of prudence.

As education secretary, Bell ranked 16th in the order of presidential succession. The order starts with the vice president, speaker of the House and president pro tempore of the Senate before descending to the Cabinet in the order that the departments were created. Derwinski, who got the stay-away order last year, ranks last -- 17th under the current order of succession.

"I wasn't disappointed," Derwinski said yesterday. He had attended Bush's 1989 speech as secretary-designate of the new Department of Veterans Affairs. "I knew it happened and that we {the VA} were the junior department. . . . All other things were equal, the junior department should be the one to service the needs of the others."

Typically, great secrecy surrounds the selection. Cabinet officers are told they cannot alert their staffs and to keep their plans for the evening confidential. Only after the speech are they allowed to tell friends and staff why they were not at the Capitol dutifully clapping for the president.

Neither White House officials nor Raymond W. Smock, historian to the House of Representatives, could say how far back the practice goes. But Smock said it could not date beyond Woodrow Wilson.

Wilson resumed the practice of delivering the State of the Union address in person, a practice that had stopped with Thomas Jefferson, who considered the idea "too imperial" for America, Smock said.

Whoever has been designated to miss tonight's speech will miss going through an extraordinary amount of security. Secret Service agents are said to have given special briefings to all Cabinet officers and directed them to appear early at the Capitol. Sharpshooters with night-vision goggles are expected to be stationed on rooftops near the Capitol.

Derwinski said he will attend the speech. "They said this happens only once," he said. "I've paid my dues."