All the way downtown in the car, Emily Bruce tried to learn the man's name. Her mom kept repeating it, and Emily seemed to be listening carefully. By the time Terry Bruce led his family through the wrought iron gate, the Bruces thought little Emily had the name down pat.

But then they went in the door of the White House and there were policemen all over and "Visitor" badges to put on and secretaries checking their names and it was all to much for a 6-year-old. When the family wass ushered into the big office, Emily just forgot.

It didn't matter, though, because Walter F. Mondale came right over and introduced himself. He said that he had a little girl, too, and his girl had a horse, and the horse liked to eat all the time, and so on, and so forth.

"It turned out to be real fun," Emily recalled happily the next day. "Except he never did show me that horse.

"if or Emily's father, Terry Bruce, too , the family's excusion to Washington last week was "real fun" - and a little breathtaking. Bruce, a young lawyer and state senator from Olney, Ill., was flabbergasted to find that, in the Washington political whirl, he had become an overnight V.I.P.

Two weeks ago, Terry Bruce won a four-way election to share the Democratic nomination for Congress in Illinois' 22nd district. The victory effected a dramatic change in his political status: the obscure Illinois officeholder became a figure of important to the Democratic Party and all sorts of national political organizations.

The Bruces felt that change when they drove here last week for spring vacation.

The family had its sightseeing all planned. Emily wanted to go to the top of the Washington Monoment; Terry was eager to tour the Capitol; his wife, Charlotte, had a yen to visit Canal Square, the Georgetown shopping arcade, because she had read in the New Republic about the arcade's architect, Arthur Cotton Moore.

But the Bruce found that other plans had been made for them. They were invited to President Carters briefing on the urban aid program They visited a top White House aide and the House majority whip. And Tuesday morning, the Bruces were the personal guests of the Vice President of the United States.

Finally, there was meeting after meeting with Democratic Campaign strategists.

The Democrats had been dismayed last fall when George Shipley, the 22nd District's popular Democratic congressman, announced that he would not seek reelection in 1978. Some party strategists had almost conceded that the conservative district's seat would be lost to the Republicians. The emergence of Bruce, a pleasant, energetic campaigner, gave the party real hope for salvation.

The political organizations, including the campaign arms of various unions and independant groups like the National Committee for an Effective Congress, were interested not only out of affection for Bruce, but also because of their aversion to Dan Crane.

Crane, an intense yet friendly dentist from Danville, Ill., won a big victory in the 22nd's Republican primary and will face Terry Bruce in the Nov. 7 election.

Crane is an outspoken member of the Republican Party's Reaganite wing. During the campaign, Crane made it clear that his political views parallel precisely those of his older brother, Philip, a congressman from the Chicago suburbs who is one of the most conservative men in Congress.

For most unions, and for other liberal political organizations, one Crane in Congress is more than enough.

Terry Bruce was important as the alternative to a second Congressman Crane.

Bruce had one other distinction, of sorts - one that Mondale hit on during the family's White House visit. "You're breaking the rules," the vice president said, in mock sterness. "No Democrat is supposed to make the front page of The Post more often than Jimmy Carter."

Because of The Washington Post's coverage of the 22nd District's election, Bruce was known wherever he went in Washington. Political types he had never met treated him like an old acquaintance, offering inside observations about the Illinois campaign. (Crane had reported a similar phenomenon after a fund-raising visit to Washington during the primary campaign).

Thus Bruce found a friendly reception last week at places like the International Ladies' Garment Workers Union, the Communication Workers' Union, and assorted Democratic party campaign units. There were no outright commitments of campaign contibributions, but when the Bruces left town for the long drive back to Olney, they were fairly confident that funds would be forthcoming.

"I've played the money game in Springfield," Bruce said. "You'd be surprised - it's important that they know you.

"If it comes down to me and some guy in Idaho or something who's just a name on the list, they might say, you know. "Oh, yeah, Bruce, we know him - he's that guy out in Illinois. Let's help him."

Dan Crane and his family, meanwhile, had headed in the opposite direction after they absorbed the joyful surprise of Crane's big win in the GOP primary.

The Crane set off for a skiing vacation in Colorado, and for the candidate it was a long-awaited balm.