Jet crisis abruptly changes Washington mood

Washington looks the same, but there has been a startling change of mood - almost as abrupt as when the crowd sang ''God Bless America'' outside the iron fence of the White House in 1941, the night of Pearl Harbor.

Some people believe they can tell the mood of the nation by the little crowd that always collects there at moments of crisis. It marked a crisis at Pearl Harbor; when FDR died; when Kennedy was shot; when a Soviet warplane shot down a Korean civilian aircraft last week with a loss of 269 lives. Rarely does it say anything; it just peers in, wondering.

The unbelievable news broke in Friday's headline: US Says Soviet Downed Korean Airliner 269 Lost; Reagan Denounces 'Wanton' Act

In Lafayette Park, three of the five permanent chess tables are occupied. Geraniums splash color, but the grass is brown from one of the driest summers in history. Pigeons perch on Andrew Jackson's head, whose horse seems endlessly to leap into the air. What's this? The White House flag is at half staff. The police are getting ready for a demonstration. And there the little crowd is, waiting and looking and wondering outside the iron fence. The crowd is there as surely as the crisis that created it.

Inside the White House press room, deputy press secretary Larry Speakes is concluding a press conference. There are eight rows of cushioned seats, six in a row, for reporters. Mr. Speakes stands on a platform before a blue curtain. Yes, he says, the President is cutting short his vacation. He sees need for world action. The questions trail off into world subjects - Latin America, Lebanon, the astronauts. There is excitement everywhere. Then Speakes says that will be all for today: ''The lid is on.'' We go back outside.

The little knot of people is still looking in through the fence, but now the excitement is in the street. It is a demonstration against Russia by Koreans, hastily organized. Their out-of-town buses line the side streets. They are angry people. They carry banners. They are friendly with the police.

The wilting heat presses down. It will be like this for several days. The placards say ''Andropov is Killer'' and ''Communist Cowards.'' Some of the banners on cloth could stretch across a street. Mostly the crowd sticks to the park and chants responses to a leader. Only two of the chess tables are now in use. What is happening in Moscow now?

The press learns President Reagan will address that the nation Monday night. He speaks at 8 o'clock and the country listens. The President is grim but restrained.

For the first time he plays a tape and reads a transcript described as the conversation of the Russian pilots who participated in the downing of Korean Air Lines Flight 7. The heavy voice of an SU-15 pilot, speaking in Russian, says: ''I have executed the launch.'' Then, ''The target is destroyed.''

He adds: ''I am breaking off attack.''

Quiet comes back to Pennsylvania Avenue. But sightseers still peer through the iron fence and look silently at the big mansion inside.