It was not for the sweet rolls that 100 people shoehorned themselves into a suite at the Pittsburgh Hilton Saturday morning.

It cost $250 a head, and it was that glorious half-second, when you could shake hands with the vice president of the United States, and then go home and tell your friends you had breakfast with him, that they made it all worth while.

That was a fund-raiser for Rep. Doug Walgren (D-Pa.) And here is Mingo Junction, "where nobody's visited since George Washington," according to the mayor, it was again Mondale an hour later, this time at a $25 a head fund-raiser that grossed about $17,000 for Rep. Douglas Applegate (D-Ohio).

And so it was the night before in State College, Penn and later Saturday in Evansville, Ind., and Youngstown, Ohio. In a matter of hours Mondale had helped raised up to $150,000 for various candidates.

In many instances, the sums will amount to one-fifth to one-quarter of the candidate's campaign treasury.

Walter Mondale has left a trial of brimming campaign kitties across the country and at the same time a growing list of politicians just a little bit more committed to the Carter administration than they were before.

He has become the Democratic party's most active campaigner in this election. He has visited 36 states since January, for nine gubernatorial canidates, 17 local and county office-seekers and 24 state part, organizations.

What's more, the unanimous view of those he's helped is that he's been a hit. Walter Mondale is one very smooth operator.

When he arrives for a campaign appearance, this politician does everything right, they say. He doesn't call a state senator a mayor or a mayor a councilman. He knows whom he's supposed to praise him or her for and how to pronounce the name.

When he leaves, often after just 10 or 20 minutes, no one is embarrassed. They have raised thousands of dollars, gotten loads of free publicity, and revved up their campaigns.

The benefits to the Carter administration of Mondale's campaigning and of the hundreds of coordinated appearances by other administration spokesmen during this midterm election are obvious, says Tim Kraft, the White House official overseeing the political activity.

"It does improve the sense of good will" to the administration, Mondale said in an interview.

But "It's not a quid pro quo. I don't believe in that stuff," he said, noting that Rep. Joe Ammerman (D-Pa.), for whom he campaigned Friday night, has been opposing the administration on the energy bill.

Mondale also acknowledges - reluctantly - that it will improve the sense of good will toward Walter Mondale, a potential presidential candidate in 1984.

A part of the appeal that draws people is clearly the vice presidency. Stephen Young, who attended the $250 reception in Pittsburgh, said he came in part because "It was an opportunity we never would have had otherwise to meet the vice president. I brought my wife for the occasion."

But Mondale's style has also made him a star on the circuit.

"He looked so good and sounded so good and he said absolutely all the right things," said Paul Pendergast, campaign manager for Kansas senatorial candidate Bill Roy, for whom Mondale drew 800 people at $25 each last July.

"The vice president told them he knows Bill Roy personally," Pendergast said. "He said the administration would listen to Bill Roy in Washington. He recognized all the right people and he even congratulated Virginia Docking (the widow of former Kansas Gov. George Docking) on her recent remarriage. It was clearly the best even we've had."

"He was a tremendous draw," said Martin Franks, administrative aide to Sen. Patrick J. Leahy (D-Vermont) of Mondale's visit to that state earlier this year. "There was this aura of being around the vice president. Neither the president nor the vice president get to Vermont very often, and we got a great deal of media coverage."

Mondale's speeches are short and punchy and require a minimum of prolonged concentration from audiences who are basically looking for a good time. His jokes are often extremely funny - evoking belly laughs - and his lines are delivered with the timing of a Johnny Carson and the facial expressions of a Jack Benny.

On serious subjects, he can soar, like his mentor the late Hubert H. Humphrey, often over the same types of liberal causes. But he doesn't try to sustain that level of intensity for more than a few seconds at a time.

The style is getting favorable reviews. "He's a much more polished speaker than I remember four or five years ago," said Keith haller, campaign manager for Montgomery County congressional candidate Michael Barnes, for whom Mondale spoke several weeks ago. "He's added a much more humorous touch to his presentation and is able to pick up nuances in a room and add to them."

And he gushes praise for the candidates. "Rep. Joe Ammerman is one of the most gifted, decent and most influential members of the House," he says in State College. "Rep. Doug Walgren is one of the truly exciting members of the House, committed, energetic and progressive," he says in Pittsburgh. "Doug Applegate is one of the truly outstanding members of the Congress and a good friend of mine," he says in Mingo Junction.

Mondale generally visits areas where there is meaningful GOP opposition to the Democrats. His speeches focus sharply on what he perceives as the Republican's most frequently invoked weapon, taxes and the Kemp-Roth bill. He tells audiences that Kemp-Roth is the most "outrageously inflationary" proposal he has ever seen in Washington and that "if you buy it, I'd like to sell you some costume jewelry."

He tells them how the administration has cut unemployment and how it has cut "the largest peace-time deficit in history left over by the Republican administration," and how they have reorganized the bureaucracy and eliminated unnecessary rules and regulations in government.

In Youngstown Ohio, still suffering from layoffs in the steel industry, Mondale does not dwell on the Middle East peace negotiations. "That town is stricken," he said. "That's what they want to hear about, how we can help them."

He is careful not to draw the candidate too close to the Carter administration, for there are danger areas in every district. He tells audiences, instead, that the Carter administration doesn't want "yes men. It wants people who exercise their honest judgment."

When Mondale went to Montana for Senate candidate Max Baucus "there was some question about whether it would be an asset," recalled Bob Fitzerald, the Baucus campaign manager.

"But it was the largest political fund-raiser ever held in our state. We raised $84,000.

"Ou fund-raiser was in the summer, and it gave the campaign early money. And when you get early money, you can buy the best available spots on TV and radio," Fitzgerald said.

Mondale withdrew from his own presidential racein part because he said he didn't like campaigning, going from Holiday Inn tto Holida Inn.

"I fell better about it now," he said.