He has become the black-knight darling of Doonesbury, a regular in Johnny Carson's monologues and the favorite bad-guy caricature of editorial cartoonists from coast to coast.

His reputation, deserved or not, as a man who would make Bambi a trophy on his office wall, has spawned a cottage industry for his opponents, who churn out T-shirts and bumper stickers emblazoned: "Watt? Me Worry?"

But if Interior Secretary James G. Watt, the most controversial member of President Reagan's Cabinet, has environmentalists worried, he is becoming the toast of another group: Republican money-raisers taking aim on next year's congressional elections.

Some GOP money men say Watt is the best fund-raising draw they have, other than Reagan. And one of his top aides confirmed yesterday that Watt will spend more time out raising Republican campaign money than he will in his Interior Department office the rest of this year.

Doug Baldwin, Watt's assistant secretary for public affairs, said Watt has fund-raising appearances scheduled in North and South Dakota, California, New Mexico, South Carolina and Louisiana in the next month. Baldwin also said Watt is spending two or three nights a week at fund-raisers here.

Watt's heavy political schedule is a complete turnaround from his early tenure as interior secretary. For almost six months, Watt turned down all out-of-town speaking engagements as he attempted to put his own, controversial stamp on the Interior Department.

His early actions drew strong fire from environmentalists, but also apparently set the stage for his new role as a GOP hero on the rubber-chicken circuit.

"Frankly, we're delighted every time every time Doonesbury comes out and hits him again," Baldwin said. "It's making him a folk hero."

Watt, obviously, is not a folk hero with all the folks. But his outspoken policies on the development of the nation's natural resources place him in the middle of one of the biggest money games in America. That apparently is paying off at political dinners.

A spokesman for the Republican National Committee said Watt has raised more than $400,000 for the committee in the last six weeks and that he is a "tremendous draw, one of our top requests" from office-seekers.

Republican polls are showing that Watt's combative flair cuts both ways politically, polarizing groups into strong support and strong opposition. It's the strong support that has Watt packing them in at Republican fund-raisers, just as the strong opposition will pack Washington with environmentalists next week.

In an assault organized almost like a Vietnam war protest, environmentalists from 50 states are to storm Washington with a million signatures on Sierra Club petitions asking Reagan to fire Watt.

Watt's emergence as a drawing card at Republican fund-raising functions came during a month-long, late-summer western trip Watt designed to shore up his image at a time when it seemed most tattered.

At the time, some of Watt's policies were being revised rapidly in response to heat in the courts and in political circles.

He was embroiled in nasty battles with House Democratic leaders and was trying to calm down California Republicans worried about his offshore oil-drilling policies. Rumors circulated that the White House was warning him to back off, especially with the 1982 elections nearing.

In his native Rocky Mountain West, however, Watt mixed scenic tours of national parks with hard politics at fund-raisers in Montana, Utah, Idaho, Arizona and New Mexico. Local politicians estimated that the Watt appearances added 15 to 20 percent to the expected take.

Since then Watt has raised money in Maryland and Pennsylvania, and plans a major southern swing next month. Baldwin said the pace -- at least half Watt's time going to money-raising for the rest of the year -- will continue after a short lull before the campaign season moves into full swing next year.

Last week Watt addressed 9,000 regular Republican donors at a dinner in Long Beach, in California, a state where Republicans seemed more worried about him than wanting him just months ago.

"They're raising a lot of money out of James Watt," Baldwin said of the environmentalists. He did not find it necessary to add that Doonesbury and Johnny Carson just seemed to be good for business, all around.