Ronald Reagan didn't bother to say good morning, or apologize for interrupting breakfast when he telephoned Dave Durenberger the other day. The president had just read the morning newspapers, and was upset.

Why, he asked, had the Minnesota senator referred to some of the president's arguments for "New Federalism" as "baloney" and "about the thinnest dodge I've ever seen?"

Durenberger soothed the president's hurt feelings by assuring him that his speech before the National Association of Counties wasn't nearly as critical of the president as news accounts suggested and that the president would see this if he read all of it.

Reagan had reason for concern. Durenberger is chairman of the Senate subcommittee on intergovernmental relations, making him a Republican the president desperately needs if his New Federalism proposals ever are to become reality.

Durenberger, however, has been giving the White House fits all year. He's said Reagan's energy policies are wrongheaded. He's recommended that the president cut as much $53 billion from his defense budget over the next five years.

And when hundreds of shouting demonstrators greeted Reagan outside a Durenberger fund-raiser in Minneapolis last winter, the first-term Republican not only refused to condemn the protesters, but in an echo of Hubert H. Humphrey years ago, he said that if he wasn't a senator, "I'd be out there demonstrating myself."

The irony is that Durenberger, a former corporate lawyer, isn't a grandstander or a maverick. He's a highly regarded moderate, who has supported the administration's tax and budget cuts.

But Durenberger, 47, also is a pragmatist, a Republican running for reelection in a Democratic state. His political sense tells him to stay close enough to the Reagan administration to reap its benefits but far enough away to avoid its liabilities.

Durenberger was elected with widespread Democratic support on Nov. 7, 1978, to a four-year term to fill the seat vacated by Humphrey's death.

It is hard to imagine two more different personalities. Humphrey was effusive and emotional; Durenberger is a mellow pipe smoker, low key and analytical. "He's always complaining that he doesn't have any charisma," said one aide.

Humphrey wore his heart on his sleeve; the greatest criticism of Durenberger is that he lacks "fire in the belly." Humphrey immersed himself in broad social policy; he wanted to remake the world. Durenberger is passionately interested in the structure of government; he wants to make it work better.

Hardworking and affable, he is a man hard to pigeonhole. He often appears to be different things to different people.

The Minnesota chapter of the Sierra Club, for instance, named him its "environmentalist of the year" in 1981. Yet during the last four years he has received more campaign contributions from groups affiliated with the nation's five worst corporate polluters than any other lawmaker, according to a study by Environmental Action, another conservationist group.

He has been praised by women's groups for supporting the Equal Rights Amendment. Yet he opposes legalized abortion, which sets him at odds with these same groups.

He complains that the public has the perception that the Reagan administration favors the rich at the expense of the poor. Yet he led a successful fight in the Senate Finance Committee against attempts to eliminate "safe harbor" tax leasing provisions, which allow corporations to buy and sell tax breaks.

So who and what is David F. Durenberger?

"He's a pro-life feminist," said John Riley, his chief legislative aide.

"He's a very ambitious guy," said a fellow Minnesota Republican, Sen. Rudy Boschwitz. "He's made a mark by not being very doctrinaire. Unlike some politicians you can't tell where Dave Durenberger is going to come down on an issue. He's a moderate, a person in the middle, the mainstream."

"His viewpoint and style fit very well into what a majority of the Senate expects; he votes straight down the middle," said Sen. Richard G. Lugar (R-Ind.,) his next-door seatmate on the Senate floor.

Tall and handsome with silver-gray hair at the temples, Durenberger came to Washington as an unknown quantity.

He was a political accident. He'd wanted to be governor, and campaigned for that office 13 months before shifting to the Senate race to allow former Republican congressman Albert H. Quie to run for governor. Both, along with Boschwitz, were swept into office as part of the GOP's 1978 "Minnesota Massacre" in which they won most of the statewide offices.

Durenberger had no set agenda. But he quickly established himself as a serious legislator by taking the lead among freshman Republicans in setting up a series of briefings on the then-pending strategic arms limitation treaty with the Soviet Union, becoming one of the better informed Senate newcomers on the issue.

He has almost a love-hate relationship with Reagan. A fiscal conservative, he and the president are on the same wavelength on many issues. He thinks the same political forces elected both him and Reagan.

He has supported the administration on most tax- and budget-cutting votes, and few, if any, Republicans have received more reelection help from the administration. Reagan, Vice President Bush and Treasury Secretary Donald T. Regan have appeared at fund-raisers in his behalf.

But he has not hesitated to cross the administration, leading one longtime Reagan supporter in Minnesota to say: "I wish Durenberger would get his head screwed on right."

For example:

In 1981, only three other Republican senators voted against the administration more often than Durenberger, according to a study by Congressional Quarterly.

When Reagan gave a speech last September calling for an additional 12 percent cut in all federal programs except defense, Durenberger quietly began work on a defense "white paper." The result, released the week after Reagan appeared at a fund-raiseer in Minneapolis, was a widely acclaimed, 195-page critique of defense spending, which proposed cuts ranging from $26.9 billion to $53 billion over the next five years.

When the administration announced a new executive order clamping down on the disclosure of government activities, Durenberger, a member of the Senate Intelligence Committee, condemned it as a "disappointment" that would result in "the classification of information that ought to remain public." He then began drafting legislation to remove the Freedom of Information Act from presidential intrusion.

But the issues that command his greatest attention are the kind that put other legislators asleep, such as revenue sharing, New Federalism and "private sector initiatives."

Last year, he led the fight in the Senate to retain federal revenue sharing for cities and counties. When Reagan first offered his New Federalism proposals last winter, Durenberger, who chairs the subcommittee which will consider them, countered with his own proposal.

He's spent months since then negotiating the issue with the White House, and was considered an ally of the president's program by Richard S. Williamson, the White House intergovernmental adviser.

That's why his comments to county officials last week in Baltimore were so significant. "He's highly respected and has a first-rate mind," said Stephen B. Farber, executive director of the National Governors' Association. "He thinks New Federalism ought to be viewed as a decentralization tool, not as a budget-cutting one."

In his speech, Durenberger embraced the concept of New Federalism, but charged that the administration's proposals to transfer federal programs to state and local governments shortchanged these governments and failed to protect benefits now received by the poor.

He also ridiculed arguments that Reagan has made to justify these shifts. "That the national government usurped its powers from its creators the states is, of course, baloney," Durenberger said.

The "big question" of the election year, he said later, is: "Does this administration--does my party--care about the poor? Is the New Federalism a smokescreen for a repeal of the New Deal? Is the private sector initiative a fig leaf to cover a lack of compassion?"

Durenberger said he believes the Reagan administration does care about the poor, but his speech illustrated a fundamental difference in outlook and background from the president.

The first Republican senator to take office from Minnesota in 20 years, he is the product of a progressive political tradition, and of a state party that renamed itself the "Independent Republicans" during the 1970s to distance itself from the Watergate scandals.

He grew up among Benedictine priests and nuns on the isolated, wooded campus of Minnesota's St. Johns University, where his father, one of the few Republicans on the faculty, was athletic director.

Like Reagan, Durenberger's first experience in government was at the state level. He was the top assistant to then-Minnesota Gov. Harold LeVander (R) for four years. The two had worked in the same small law firm--one that decades before had produced another Minnesota governor, Harold Stassen, the perennial presidential candidate.

After LeVander left office in 1970, Durenberger took a job with H. B. Fuller Co., a glue manufacturing firm in St. Paul headed by still another Republican former governor, Elmer L. Andersen.

He married Penny Baran, a former Humphrey assistant who remained an active Democrat until 1978. His first wife died of cancer, leaving him with four children, all under 7 years old.

This was a time of great debate about "corporate responsibility" in Minnesota, and Durenberger became "almost a professional volunteer" for the Fuller organization, his wife said.

He was a joiner--a county park commissioner, a hospital board member, a United Way fund raiser, and director of Public Service Options, an industry-sponsored group seeking ways to involve business in delivering social services.

Durenberger said his experiences in those years convinced him the federal government has much to learn from state and local government as well as business.

His first legislative effort, and the one he has spent the most time on as chairman of the Finance subcommittee on health, was based on his experience with flourishing Health Maintenance Organizations in Minnesota--a bill to promote competition to help control runaway health care costs. It would give tax breaks to companies that offer workers a choice of health plans. The idea would be to force doctors and hospitals to offer better care at a more reasonable price.

This is the kind of problem that Durenberger believes he and Reagan were elected to solve by changing the role of government. Unfortunately, he said, the administration has failed to move its focus away from budget and tax cuts.

This causes problems for incumbents like Durenberger. In a year when the hard-pressed Midwest looks like a disaster area for Republicans, he is in an unusually strong reelection position.

But he is still worried. His chief Democrat-Farmer-Labor Party opponent is Mark Dayton, a wealthy department store heir, who already has spent $3 million of his own money on the race.

Dayton, Durenberger said, "isn't running against me. He's running against Reaganomics."

"Those of us up for reelection," he added, "are trying to say there is more to Reaganomics than cutting taxes and budgets."