Things happen very fast in Washington.

A few months ago everyone was asking: "Will Teddy Kennedy run in 1980?"

Now people want to know: "Will Jimmy Carter run in 1980?"

At the moment it is very hard to predict. There has been a great deal of pressure on Carter to run, particularly by members of his staff. But insiders say he is reluctant at this time to announce his candidacy.

Carter has told friends, "If I challenge Kennedy in 1980 I could split the party. Besides, there are many family considerations that I have to resolve."

One is whether his wife Rosalynn wants Jimmy to run for president. Intimates say that Rosalynn, who has never enjoyed the give and take of national politics, would prefer that Jimmy go back to the U.S. Navy. Most of Carter's Annapolis classmates are admirals now, and Rosalynn is sure that if Jimmy would reapply for his commission he would earn his flag rank in no time.

On the other hand, some friends say that Rosalynn enjoys being first lady and much prefers the east wing of the White House to the grand ballroom of the Carter peanut warehouse in Plains.

Another family consideration that Jimmy is seriously weighing is whether, by not running, he'll have to take his daughter Amy out of the District of Columbia's school system. One of the reasons Jimmy gave for wanting to be president is that he had heard the D.C. school system was so much better than the one in Americus, Ga.

A third family consideration Jimmy has to face up to is how his brother Billy will feel about him running for another term.

Billy has always been shy by nature and hated the limelight, and he has never cottoned to his brother being president of the United States. He was once overheard to tell Jimmy: "I'll be glad when you're out of the White House so I can get back to tending my gas station. Everyone who owns a station has been making a mint. But not me. Every time I want to go to work I get called in front of a grand jury. If you cared anything for me you'd chuck it all and get the feds and press off my back."

The most important factor in Jimmy's decision will be how his mother feels about him running for president. Miss Lillian has yet to indicate if she will give her permission or not.

"I've tried to give Jimmy a good upbringing and teach him right from wrong," she told the Muppets on television the other night. "But the trouble with being president of the United States is that you don't know what is right or wrong. When you think you're doing right, the public says you're doing wrong. And when you're doing wrong, the public says you're doing right. I've never stood in the way of my children. So if Jimmy wants to run for president it's my duty as his mother to support him, even if it's difficult to explain to my friends whose sons are all successful in their own fields. On the other hand, if he wants to buy a cooperative apartment on Fifth Avenue in New York, I'll go along with that too."

Most of the pressure on Carter is coming from his close advisers who keep telling him, "Some people will say it's unfair of you to challenge an incumbent senator from Massachusetts when he decides he wants to be president. But these are not ordinary times and the country needs leadership. You're the only one who can do it after what we've gone through for the past three years."

Pretty soon Jimmy Carter will have to make the hardest decision of his life. Will he enter the presidential sweepstakes and risk splitting his own party by challenging Kennedy? Or will he bow out and wait another four years to run, when the Democratic nomination would be his for the asking?