Transportation Secretary Neil Goldschmidt, once a big-city mayor, comes from the school of politics that says you take credit for your successes, cut your losses, care for your friends and punish your enemies.

As a new guy in town this fall, Goldschmidt was appalled when Vice President Mondale, not President Carter, announced that the Interstate Commerce Commission had ordered service restored on the stricken Rock Island Lines.

"Here the president had just saved their railroad," Goldschmidt complained, "and he wasn't out in front saying, 'Look, I saved your railroad.'"

A few weeks later the same Neil Goldschmidt told the world that Chicago Major Jane Byrne was untrustworthy, an assessment, he said later, was based on "a personal problem," but one he announced after she had switched her allegiance from Carter to Sen. Edward M. Kennedy (D-Mass.) in the battle for the Democratic president nomination.

Goldschmidt's comment was widely interpreted as a threat that he would cut off millions of dollars in Department of Transportation grants to Chicago because of Byrne's untrustworthiness. It was also widely interpreted in Washington as a threat to other big-city mayors, most of whom have endorsed Carter, to stay in line.

In fact, DOT grants have continued to flow to Chicago, to Boston and to other parts of the country in the normal course. Actually, $1 of every $5 in discretionary money that DOT has distributed since Goldschmidt became secretary has gone to Chicago and Boston.

Nonetheless, the perception is that a message has been sent.

"I think Neil hammered it on the door," said an official with close ties to many mayors' offices. "Mayors had already heard the positive things" about the Carter administration.

Whether Goldschmidt sought the job of message-carrier for himself or was ordered to it, it is clear he was willing.

When he came to town, fresh from the mayor's office in Portland, Ore., he told reporters that Carter had done more as president in his first year to help cities than the previous three administrations had, but that nobody knew it except the mayors.

Goldschmidt, 39, made no secret of his feeling that Carter's organization needs to do a better job of advertising, selling itself and, perhaps, of using its advantages of incumbency a little more strongly. He referred to himself in one gathering as a member of the "political arm" of the Cabinet.

"When I was first elected in Portland I though that if we did a good job, people would notice it and I would be reelected. Then I took polls." He realized then, he said, that part of the job of politics was sales.

The flap over Mayor Bryne created some uncomfortable moments for Goldschmidt. He said several times that he wished he had made clearer that his problems with Bryne did not mean that he was going to do something illegal and deprive Chicago of money it needs. But it has not harmed his good standing with the Carter-Mondale campaign committee.

When Carter canceled his personal appearances during the week of his official announcement for reelection so he could watch Iran, Mondale replaced Carter, and Goldschmidt replaced Mondale in appearances at Philadelphia and Miami. Goldschmidt is Jewish, and is known to be concerned about the rift between the Carter adminstration and many members of the Jewish community.

About the first question Goldschmidt was asked when he came to Washington in August was, "Are you gong to campaign for President Carter?"

"You bet," he said.

Robert Ames, a senior vice president of the First National Bank of Oregon, who is winding up a tour here as a special assistant to Goldschmidt, calls him "one of the best salespeople I've ever met. Jesus, he can sell. Sometimes the force with which he says things is so convincing you have to back away and look at it again to see what you really think."

Goldschmidt was elected to the Portland City Council once, and was twice elected mayor. He is forceful, dynamic, articulate and handsome, a nice man to have on your side during a campaign. He commands intense loyalty from those who are close to him, and has scared the living daylights out of a few entrenched bureaucrats over at the department because he doesn't always think their way, and he may, just may, know how to get a few things changed in the short period of time he says he expects to be in Washington.

The Portland that he left was a substantially stronger city than it had been when he was first elected mayor. He campaigned on preserving neighborhoods and reviving the downtown, and he appears to have achieved those aims, or at least to have started action in that direction.

When he took the mayor's office in 1972, one of the long raging controversies in that city had been whether to build interstate highways through Portland.

Doug Wright, Goldschmidt's planning director in Portland, now a top aid here, recalled that "Neil went around saying, 'We've got to stop that freeway.' For a long time we didn't know if we were going to be able to, but we did."

The freeways were modified or eliminated, and the federal aid scheduled for them was transferred to other projects, including a downtown transit mall, another controversial project.

Two Parallel business streets through the Portland core were closed to all but buses and pedestrians, sidewalks were widened, trees weree planted and the bus lines were rerouted so that every line in Portland would come down those two streets. There was substantial downtown disruption while that occurred, and substantial grumbling.

Now that is over, and Portland is proud of its new downtown.

Bob Hazen, chairman of the board of Ben Franklin Savings and Loan, was not all that excited about the transit mall concept. "We were thinking of taking our office out of downtown and going to a suburban location. Goldschmidt called and said, 'No way.' We had mixed emotions about leaving, too, so we stayed.

Hazen is a political opponent of Goldschmidt, and has backed candidates to run against him. He found it a tough course. "I lost some money," he said, "and a lot of time.

Banker Ames and Goldschmidt disagreed on Portland television about whether Portland needed a convention center. Goldschmidt said yes, Ames no. The disagreement continues. Yet Goldschmidt brought Ames with him to Washington to help on such problems as Conrail and Washington National Airport.

"There is no one I know I would come here to work for other than Neil Goldschmidt," Ames said. Ames, a Republican, cites two "all-pervading thoughts" when he was asked to describe Goldschmidt:

"He is very fiscally responsible, which tends to sit well with the business communiy. He is honest. That sounds trite, but he's got that image in Portland, and people who have opposed him say he is honest."

Goldschmidt is a dynamic, witty speaker. A delegation of Maryland legislators, most of them Republicans from the eastern shore or western Maryland, visited Washington recently to learn about the Metro subway funding problems.

Goldschmidt spoke at lunch, told a few jokes and talked about the necessity for aiding cities and mass transit.

"The best thing Carter could do,' one eastern shore legislator said to another as they were riding the elevator at Metro, "is let Goldschmidt do the talking."