PRESIDENT REAGAN did not go horseback riding in the Virginia countryside last week, signaling that something was very wrong in the nation. In fact, things were so serious that the president spent most of Wednesday afternoon--the time usually reserved for playing cowboy--with his advisers trying to figure out what the trouble was. This proved considerably more difficult than mastering a hurdle.

Reagan, dressed in his jodhpurs and $1000 riding boots, entered the cabinet room, where various advisers and cabinet officers were assembled, grim-faced, around the table. "I'm sorry about that plate, dear," Reagan said to his wife, who had followed him into the room.

"Don't worry Ronnie, we have 199 more." She motioned him into his chair. "Now you just sit right there and listen to these nice men."

"Thanks, honey. Oh, are you going riding with me this afternoon?"

"No, Ronnie, not today. You know how it messes up my hair. I think I'll spend the afternoon talking on the phone with my friends from California."

"Well, have fun, Jane," the president smiled.

Nancy laughed. "He's such a practical joker," she said, leaving the room.

"What a girl, that Jane." The president looked at the men around him. "Well, who's going riding with me today?"

Edwin Meese delivered the bad news. "I'm afraid you can't go horseback riding today. Mr. President. We have too many important problems to discuss this afternoon."

Reagan frowned. "Aw, shucks, Jim, can't you discuss them without me?"

"My name's Ed. Mr. President. I'm sure we could handle these matters without you, sir, but the press might see you leave the White House if you go riding. Maybe if we finish early, you can go before dinner."

This possibility seemed to satisfy Reagan, who began doodling. "Mr. President, I think you need this," said Alexander Haig as he pushed a White House memo pad under the president's pencil.

"Thanks, Cap," Reagan said.

Meese started speaking. "In the vice president's absence, I will conduct this meeting."

Haig interrupted. "Who put you in charge, Ed? The president is here."