While time and the Potomac air often erode the candor from many of the high-minded political appointees who come here, it's much too early to judge if Washington will change John R. Norton, the new second-in-command at the Agriculture Department.

Not to worry, say the people who know him best and the lobbyists who watch him closely. Forthrightness, apparently, is Norton's stock in trade and no one doubts his political aplomb, even though this is his first job in government.

For now, Norton, a 56-year-old Arizonan who has done well for himself as a farmer, is nothing if not candid: so painfully candid that he wonders aloud if he can survive in Washington's piranha politics.

"People in our trade are almost shocked by his candor and frankness," said one lobbyist. "He's a quick study, but he's walked into an administrative nightmare at USDA. It's tougher for him because there are so many seasoned people to deal with over there . . . well-entrenched people who know the routes, and the routes around the routes."

Added another lobbyist and GOP political activist: "You can disagree with Norton on philosophy or principle, but you have to respect his views because he is honest. That's important, because there's been a lot of slipping-around honesty over at the department the last couple of years."

Norton, a longtime Republican who served on the Reagan administration's agriculture transition team in 1980, was named earlier this year to succeed Richard E. Lyng as deputy secretary, the day-to-day manager of the department.

Since his Senate confirmation in May, blocked for weeks because of a GOP political squabble that had nothing to do with Norton, he has been ensconced in USDA's main building trying to parse the programs and the bureaucracy.

"Following a guy like Dick Lyng, I've got an uphill struggle. I may never have the political skill that he had," Norton said recently. "And there's no way that Secretary John R. Jack Block could have the same level of comfort with me that he had with Lyng."

In recent days, Norton's education has been confined to conducting the USDA's internal budget hearings for fiscal 1987, the process in which division heads are required to justify their spending and program ideas. Tedious as it may be, he said, it's probably the quickest road to understanding USDA's functions.

Inevitably, as rumors have intensified about a Block resignation, the farm lobby has speculated that Norton might be Block's successor. For his part, Norton will say nothing.

But an element that keeps jumping out, especially in a department where political appointees' distrust of Congress and the news media seems endemic, is that Norton is cut from a different bolt of cloth. Consider:

* When potential critics poised to pounce at his confirmation hearing, Norton easily derailed them. The issue was the roughly $2 million in surplus federal commodities he received in the 1983 payment-in-kind program. When Norton said that he actually got more than USDA's inspector general had reported, the committee left Norton alone and turned its ire on the IG's slipshod work.

* Although the committee raised few questions about it, Norton said he took full responsibility for the unfair labor practices of which his farming company was found guilty in California. The company has challenged the rulings in federal court, but Norton quelled potential controversy by delivering a stack of explanatory documents to the committee.

* When Norton came to town last winter, he paid his expenses for more than three months while he waited for his nomination to clear, rather than taking a salaried "consultancy" that was offered.

* Norton delays an interview until a tape recorder arrives. A reporter wonders why there is a need to tape. "They told me it's to see if I said what you say I said," he replies. The reporter objects, Norton turns off recorder and slides it away.

All of this is different. But then, Norton comes from a farming background and perspective unlike that of any other recent secretary or deputy. He took operations started by his grandfather and father and built a fruit- and vegetable-growing empire on 25,000 irrigated acres in California and Arizona.

The business is so far-flung and Norton's distance from a tractor seat so pronounced that he conceded it might be stretching things to call himself a farmer, at least in the traditional sense. "I'm an employer," he said.

His resume of activities -- directorships, investments and civic activism -- makes it plain that, of late, Norton has done little hands-on farming. In his current absence, a son and longtime employes oversee the lettuce, citrus, melons, celery, asparagus, cotton and alfalfa.

With his GOP background, Norton was touted for the USDA job by western growers who argued that their side of agriculture needed more representation in Washington. He already is goading departmental scientists toward more research into post-harvest handling technology for fruit and vegetables.

Norton's business success and his politics (the only member of his family to register Republican) seemed made to order for an administration with an orientation toward large-scale agriculture and the "free market" philosophy.

Norton is a certified supporter of both concepts, with some qualifications. He said, for example, that while he thinks the factory farms of the type that he runs offer consumers the best in fruit and vegetables, the USDA should do more to promote diversity in agriculture and to encourage smaller-size farmers to produce for local markets.

"Anytime something can be grown in Maryland for the Washington market, it should be done," he said. He nonetheless was pleased that his "better" California strawberries have been sold in Washington-area stores, probably more a testament to supermarket buying practices than to the berries.

And while Norton has participated in federal crop-support programs, he said he agrees with administration efforts to cut them back. Still, he says he thinks that federal programs are needed, "even in the purest free market."

"We have gotten farmers into this economic situation they're in today," he said, "and I feel government has the obligation to use some temperance in withdrawing."