It's a sometimes lonely, sometimes discorganized and distinctly underdog effort that California Gov. Jerry Brown is running these days.

He is on an 11-day swing that has taken him from the Midwest to boston and New Hampshire with occasional stops in the TVstudios of New York, while the headlines in America's newspapers have been dominated by the struggle in Florida between the other two undeclared Democratic candidates, President Carter and Sen. Edward M. Kennedy (D-Mass.).

Brown, 41, understands all this, but he has a reminder for people.

"In the year 2000," he says, "I ill be younger than Ronald Reagan is today."

Occasonally Brown talks as though even now he is looking beyond 1980. "I'm prepared to dig in," he said to reporters on his press bus. "Whatever the outcome, I'm prepared to form a long-term coalition."

No politicians rush to be seen at Brown's side. He is the outsider, and that suits him. "I consider my insurgent movement a frontal assault on the established power of the Democratic Party," Brown told students at New England College.

No matter how many people are listening, nor the odds against him, Brown is determined to carry through with his campaign, which promises a sometimes vague, sometimes apparently irreconcilable package of measures that would fundamentally change the way America is run.

"Before we can get anything done," Brown says, "we've got to involve groups that previously have been excluded" from what he calls the ruling coalition. "There is tremendous political power emerging from people like Ralph Nader, the antinuclear movement and others."

Brown favors federal government intervention in new areas and the continuation of all present federal regulatins. At times, he speaks as though he would try to do for government in the 1980s what Franklin D. Roosevelt did for it in the 1930s.

Brown comes close to advocating a public planning corporation and, although he says he hopes tariffs can be avoided, his speeches are full of warnings about foreign imports that would warm the heart of any protectionist.

"We're going to have to find out how we can take the Japanese and German experience and recreate it," Brown told reporters. He would rein in the "profiteers of the world," as he calls the multinational corporations, and introduce government more directly into business, as the Japanese and Germans have done.

He has only begun to spell out his ideas for new federal activities. So far the most detailed and striking plan involves energy.

He advocates a federal energy corporation to take exploration and development of energy resources on federal lands away from the private oil companies.

Brown would establish a national oil import authority to replace the oil companies as the purchaser of foreign petroleum. In addition, he wants an act of Congress to enable the president to appoint public members as oil company directors and set up a presidential commission to study the structure of the oil industry.

Brown's initial campaign swing through the early primary states in the East has been divided among talks to college audiences, small meetings with environmentalists and potential financial backers and television appearances.

"I'm still trying to formulate what is viable for this campaign," Brown said at one point.

"It's a marathon," said Brown's campaign manager, Tom Quinn. "First of all you get in shape for the marathon. You practice. You exercise. That's the phase we're in now."

Brown's goal in New Hampshire and next door, in Kennedy's native Massachusetts, is to finish second, ahead of President Carter. "We want to get it down to a two-person race. Then it will be up to Jerry to take on Ted Kennedy," Quinn said.

Brown appears popular with the voters under 30 and with Catholics and is working both those constituencies in New Hampshire and Boston.He also hopes that college students will hear him speak and be moved to volunteer to help build the precinct organization he plans to put together from scratch in New Hampshire.

Money is tight, and Quinn and other Brown backers know that good showing in one or two of the early primaries is important.

Brown racked up an impressive string of TV appearances, doing one Sunday network interview show, one morning talk show (both on ABC), the nationally syndicated Phil Donahue Show and the New York-based Stanley Siegel Show within one week.

He also filled the hall at each college he visited from New York's Columbia University to small New England College in Henniker, N.H. Some of the halls only held 300 or 400, but the audiences were enthusiastic and curious. At one, Keene State College in Keene, N.H., students complained that they had been steamrolled by an outside Brown advance team eager to make sure that the Maynard C. Waltz lecture hall was jammed.

Brown drew cheers for his antinuclear stand, particularly his pledge to oppose licensing the Seabrook, N.H., power plant now being built. The students also liked his opposition to reinstituting the draft and his support for the Equal Rights Amendment.

Brown's infant campaign also has its rough edges. He wanted to address a luncheon meeting organized by the New York Association of Women Business Owners and his aides said he would use the occasion to make a major speech.

The women's group then decided it didn't want Brown because it didn't want a high-powdered politican to overshadow the other scheduled speakers. Brown was told not to come, spokesmen for the association said.

The freshness and mystery that seemed to work for Brown in 1976 when he flew East late in the campaign and won the Maryland, Rhode Island and New Jersey primaries is gone now, and Brown's campaign style has changed.

"I have a more theoretical base for my campaign now than I did four years ago," Brown said. "I didn't understand as much then as I do now."

In New Hampshire he is testing whether he can make 2 political success of his conviction that the nation wants to make a serious commitment to change many traditional ways of thinking and doing business.

And he is trying to suggest that defeat in 1980 would not end that effort.