After six short weeks in office, Interior Secretary James Watt is without doubt one of the most talked-about men in town. He walks in a nimbus of stories already approaching legend. He has initiated changes in his vast domain that will keelhaul the bureaucracy and rattle papers in every corner of the country. And every one agrees on one thing: he has taken charge.

Watt, 43, told President Reagan this would happen. "I said you'll need to back me and back me and back me, and when you can no longer do that you'll have to fire me. And he said, 'I will,'" Watt recalled. "He said he'd support me because he wanted to bring change to America."

Watt, regarded by his enemies as a formidable, dangerous opponent and his friends as a forceful administrator who can and will deliver, is by his own account a man with a mission.

"In four years, I would like to have established predictability, so that when interest groups come to a conflict they'll be able to guess how Interior would come out on it," he said in an interview.

"I am a fundamentalist in economic, social, spiritual and political matters . . . in the sense of back-to-basic tenets," Watt said. That means, he added, "that I have a responsibility of stewardship greater than just for this moment. I have an accounting to the president, to the American people and to God, and I take it seriously."

The secretary is a moral man, a born-again Christian of the fundamentalist Assembly of God denomination. As though cast for a Ronald Reagan movie, he was an all-around sports hero and prom king at his Wheatland, Wyo., high school and married his prom queen, Leilani Bomgardner, 24 years ago. Religion is an important part of Watt's life. While he does not smoke, or drink anything stronger than tea, he has not removed the coffee and cola machines from his new department, contrary to rumor, nor has he posted a women's dress code of skirts and long sleeves.

Neither has he replayed the weekly lunch-hour Bible-eading sessions that a subordinate held while Watt was at the Federal Power Commission. "I never attended," Watt said. All these stories, and others, are flying at Interior, but the truth is that Watt is repeating the loner's life that irritated less zealous subordinates throughout his career.

That means he works through lunch and on weekends, runs meetings in a pressured, rapid style and cuts off chitchat in order to get home to his family. Some reported policy shifts were not Watt's doing, but suggestions from "some of the people who are trying to get noticed," according to one of those affected.

Watt shows a warm and compassionate side for his family and has loyal close friends. Sen. Alan Simpson (R-Wyo.), whose father, former senator Milward Simpson, gave Watt his first job back in 1962 as a Washington legislative aide, calls Watt "a warm, intelligent, responsive and caring human being," a theme that was echoed by western businessmen at Watt's Senate confirmation hearings.

But there are some who find themselves, at least for now, shut out on the cold side of Watt's nature: the environmentalists.

When Watt agreed to meet recently with five environmentalists, including his old Wyoming rancher friend Tom Garrett, now a conservationist consultant, it was supposed to be a get-acquainted session on wildlife issues. But it turned out a discussion that has conservationists buzzing with worry all over town.

Although those who attended won't give details about the Feb. 15 meeting, it is known Watt delivered an emotional complaint that he has been lied about, misrepresented and undermined at every turn by environmentalist groups. He was bitter about people who had testified against his nomination, particularly the Audubon Society, and told the group that environmentalists had "poisoned the press" against him. As a result, he said, they now have "a heavy burden to carry" in making their case to the Reagan administration.

"He was very candid," said Lewis Regenstein of the Fund for Animals, one of those present. "He seemed interested and open-minded on the issues, but we left with no question that he is very strongly and personally hostile to -- and very much annoyed by -- the environmental government. He's taken it personnally and we're in for some hard years."

Watt's views of environmentalists were no secret when he arrived at Interior after three years directing the Mountain States Legal Foundation in Denver. The foundation had filed many of the lawsuits challenging federal and state land use and environmental policies; Watt had spoken repeatedly of "environmental extremists" whose goal, he said, was "to delay and deny energy development." In one speech, he asked whether "their real goal" is "to weaken America."

Watt's new boss, President Reagan, has voiced a similar line. "In fairness, Watt is just doing what Reagan wants him to do," Regenstein said.

But the picture is complex. "I haven't given up on Jim Watt at all," said Tom Garrett. "Some of his reforms are long overdue. I came out of that meeting convinced he's receptive to different points of view and willing to be educated, willing to take a look at new ideas. He can be brought around."

In a 90-minute interview in which he talked about his job, his faith and his feud with the environmental movement, Watt confirmed that he feels misrepresented.

"The emotional heartstrings of America flow to this department," he said. "Anybody who's here is going to receive undue attention. . . . That's part of the turf, that's the job description."

Some environmental groups, he said, "have pronounced the public interest law movement a tool with which to reshape our political system," and that worries him. "I'm disturbed about anybody who's not trying to help us accomplish the objective of economic recovery."

"The environmentalists have taken a 20-year career and ignored 17 years of it, slamming him for Mountain States," said Doug Baldwin, who has worked with Watt since 1962. "He's got a good environmental record."

In line with GOP campaign promises, Watt has moved to speed up the schedule for offshore oil leasing; his proposal to open two California parcels over the objection of Gov. Edmund G. Brown Jr. made headlines there. Watt clamped an early hold on regulations from the Office of Surface Mining, target of major western industry complaints, and delighted western governors with promises of a new managerial approach toward federally owned land in their states.

He plans, he said, "to open up and encourage the opportunity for energy development of all types," including wind, solar and nuclear fuels.

Throughout, his theme has been that existing legislation is fine and needs only better management. Responsible growth is true conservationism, he says, because to block energy development now, as some of his critics demand, means reckless overdevelopmemt in some future energy emergency.

"We want the right kind of development to come over time, not the wrong kind of development to come in a crisis," he told his confirmation hearings.

All this is part of Watt's religious approach to his job.

"I believe there is a life hereafter, and we are to be here to follow the teachings of Jesus Christ," he said. "One of the charges He's given us is to occupy the land until He returns. We don't know when He is coming, so we have a stewardship responsibility . . . to see that people are provided for until He does come and a new order is put in place. So we cannot waste or despoil that which we've been given in the earth because we don't know our tenure here."

This calls for "a balancing act" between conservation, utilization and stewardship, Watt said, defining stewardship as carrying out one's existing responsibilities before assuming more.

"This administration will be good stewards of the land. It will be in the mainstream of the environmental movement," he said.

"He certainly knows exactly where he wants to take this department," said Russell Dickenson, head of the National Park Service and the only top bureaucrat Watt retained from the Carter administration. "Jim is a very forceful, dynamic individual. I've got great respect for him as a manager and as a person." He said Watt is highly verbal and a quick study, preferring to hear all points of view at a meeting and make decisions on the spot.

To some career bueaucrats, that means Watt is talking mainly to the people who came in with him, many of them friends and co-workers for more than a decade. The men and women who wrote the nation's parkland rules, grazing controls and recreation policies in a thousand Federal Register notices now and say they are taking orders, not making policy. The department's $1 billion budget cut was allocated with little or no input from them.

Meg Maguire, who was deputy director of the Heritage Conservation and Recreation Service under Carter, was stunned by word that her agency would be abolished.

"No one ever talked to me or the director during the transition, so I marched in and said I can't leave until someone here knows what this operation is all about," she said. "No one asked what benefits would be foregone by these cuts. There wasn't a transition."

The Land and Water Conservation Fund that HCRS ran no longer will be used to buy more parks, Watt said, but rather to refurbish existing ones. The technical advice HCRS long has offered states on preserving monuments, historic buidings, parkland and wildlife will move to the National Park Service, under reduced funding, while the program to coordinate management of the nation's coastline will end. The states can expect to receive management rights on a number of federal parks, and will get a new $50 million a year in payments in lieu of taxes on federal land, a program axed under Carter that Watt will revive.

Watt rerouted paper flows to bring more policy recommendations directly to him, bypassing consultation among departments on grounds things were getting lost and delayed at each stop. "He believes strongly in a military line of authority, a clear, clean chain of command," said Baldwin. Far from mistrusting the career bureaucrats, he said, Watt regards them "as potentially his greatest resource."

But a toiler at the Fish and Wildlife Service sees it differently: "I've lost track of what the other people are doing. There's a tendency now to burrow down and hide."

Watt made it clear in visits to the bureau chiefs that, as one staff member put it, "any leaks would be taken out of our hides." But, as ever in Washington, there are leaks and criticism and stories, and Watt, despite his experience at the FPC and earlier at Interior, still finds them exasperating. Especially when they are not true.

"There's no justification for that," he said of one false report of a massive budget cut, "except to sap my energies straightening the record out."

Some department officials find Watths brisk decisiveness a tonic after what they thought was too much compromising by his predecessor, Cecil D. Andrus. Andrus tried to avoid environmentalists lawsuits by giving them half a loaf, notably in mineral leasing and water project disputes, but he got sued anyway, these officials say. Watt can expect the same lawsuits, but he will get the whole loaf of development, according to this view.

That is just what worries the environmental community. Rafe Pomerance, director of Friends of the Earth, said Watt has lost the distinction between regulatory reform and crippling budget and personnel cuts that hamper performance of the basic agency mission.

Although Watt promised environmentalists always would get a chance to speak their piece, Pomerance signed when asked about Watt's approach to environmental worries.

"There is no approach that I know of," he said.