Rep. Morris K. Udall (D-Ariz.), who has been battling with "king copper" over proposed mining law changes for a decade, suddenly has declared the Arizona industrial monarch too ill to cope with such an overhaul and says he will withdraw his support of major mining law revisions, including his own bill.

When he was home for Congress' recess, Udall at first continued to tout his bill to place the mining of "hard-rock" minerals - copper, silver, gold and the like - on federal land under a leasing system similar to that already imposed on oil, gas and coal. It would have replaced the existing 1872 federal ming laws, which give ownership of federal land to miners who find and dig minerals on it. Those laws place few controls on miners and give them the right to extract minerals without paying royalties.

Recently, however, Udall announced at a meeting of the Arizona Mining Association here that he would withdraw his bill, refuse to support a similar Carter administration bill expected this month and throw his weight behind a bill drafted by the American Mining Congress. That bill, introduced by Rep. Philip E. Ruppe (R-Mich.), doesn't include the leasing system.

His change of heart, Udall says, was prompted by the "most serious and repressed situation in a couple of decades" in copper mining, the largest private industry in Pima County, where most of his southern Arizona constituents live. Although both Udall and industry representatives say his bill would not, in the short term, worsen the layoffs and falling prices now plaguing the copper industry, Udall said he believes it could have a bad effect "psychologically."

"The psychology of these people is very down," Udall said in an interview. "They feel overtaxed, they feel over-regulated, they feel that foreign countries are competing unfarily with copper, they don't feel the State Department's going to help them with any of these problems.

"And while all that is going on and you're losing a million dollars a day on a mine, here's your local congressman saying we're going to change the law so that you can't find the ore bodies you'll need in the future.

"It's a combination of psychological elements in which this one was assuming disproportionate size, I thought, but if people perceive something as a fact, sometimes it's just as important as whether it is a fact."

Although Udall agrees that he "gave in on the major points that we will patch up the old house and not try to build a new one," he says Ruppe's bill includes some changes he wants, such as royalty requirements.

But the fact that he gave in at all surprised many, particularly because Udall's abrupt change came at just as he'd gained the political clout - administration support and his own power as the new chairman of the House Interior Committee - to probably see his long fight for mining law revisions finally succeed.

"It's ironic and sort of disappointing to me that after working on it for 10 years, that when the climate in Washington is finally right to get it and I'm in the right position to do it, this major industry has the worst situation in a generation," Udall conceded.

He said he cedided to reverse his stand late last month after discussing the copper industry's woes - more than 6,500 workers in Arizona recently have been laid off, for example - with "good friends," including labor leaders, mining company executives and lawyers who represent mining companies. Until then, he said, he hadn't known the extent of the copper industry's problem.

Industry spokesmen say they are pleased.

"Well, well, well - how about that," said J. Allen Overton, president of the Washington-based American Mining Congress, when asked to comment on Udall's announcement. "I think that perhaps the time is finally here when the wrecking crew will quit and the construction crew can start working . . . Whatever the reasons for this change in position and the fact that he's beginning to see the light - whatever the reasons - Udall should be credited for his statesmanship in changing his mind to fit the facts."