He is the picture of the upright Yankee gentleman: blue-eyed, crew-cut, bow-tied, rosy-cheeked.

He speaks without self-consciousness of "honor in government." But the air of invincible amity covers a sharpness for facts and a passion for law that were Richard M. Nixon's undoing.

Ten years after Watergate, Archibald Cox at 70 has receded into the general background. He teaches at Harvard Law School. As he walks through the streets of Washington the day before the 10th anniversary of the break-in, he is recognized by none of the passers-by. It is only when he gets to the Dupont Plaza coffee shop that someone at a nearby table hails him. It is Derek Bok, the president of Harvard, who reminds him jocosely that he was on Nixon's enemies list.

Cox is observing the anniversary in his own way: he is explaining the significance and the consequences of those dizzy, dangerous, suspenseful weeks, months and years of cover-up, bombshells, tapes and "inoperative" statements from the "zero-defect" White House of Richard Nixon.

It was a triumph for a system that could expose wrongdoing at the highest levels of government. It was a glory of democracy. Through a random selection process, the republic produced the very people needed to save it.

Special prosecutor Cox, the star of the "firestorm" of October, 1973, meets about 20 hard-core Watergate addicts at a press breakfast and--logically, mildly--describes the significance and consequences of that hazardous, heady time.

"What if?" he is asked repeatedly. What if Nixon had destroyed the tapes? What if Alexander Butterfield had not "spilled the beans"?

"There are so many possibilities and coincidences," he observes. "What it comes down to is that we have a good fairy sitting on our shoulders most of the time."

Could Watergate happen again?

"Of course it could happen again. The abuse of power is inherent in human nature. But the immediate likelihood is reduced because so many remember it all, and the reforms which came about make it measurably less likely."

On the down side, he finds it "troublesome" that the Reagan administration is silent about the need for high moral standards, that it seeks to weaken the reforms, that it speaks disparagingly about financial disclosure requirements as "an overreaction," that the attorney general fumes about the special prosecutor act.

The whole handling of the question of Labor Secretary Raymond J. Donovan puzzles Cox.

"I don't mean to convict Ray Donovan," he adds, "but I find it disappointing, almost shocking, that when the FBI told White House counsel Fred Fielding some disquieting news about Donovan's past, Fielding said 'Don't pursue it.'

"That says something about zeal or lack of zeal for not just honesty, but honor, on the part of high government officials. I like to think I would have said, 'Run it down.' "

Fielding was "part of the Nixon period"--deputy to White House counsel John W. Dean.

"There was never anything that rubbed off on Fred Fielding, but I would have chosen someone else," Cox says.

Cox has done more than speak of the insensitivity of the Reagan White House to the Watergate experience.

Reagan has named two Watergate figures to obscure public posts: Frederic V. Malek, an aide to H. R. (Bob) Haldeman and author of the chilling "government responsiveness" memo, to the board of governors of the U.S. Postal Service, and Maurice Stans, chairman of the Finance Committee to Re-Elect the President, to the Overseas Private Investment Corp.

Cox, now chairman of the citizens' lobby Common Cause, announced immediately on hearing of Stans' appointment that he would testify against it. Various friends of Stans have importuned him to accede to Stans' oft-repeated request to "give me back my good name." Cox is adamant, and the nomination has not been resubmitted to this Congress.

"It is not good enough to say you don't know anything about the shabbiest campaign finance operation in our history," Cox says firmly.

Cox minds most the prosperity and celebrity of the richly rewarded, reminiscing perpetrators of Watergate.

"I ask myself if my Uncle Max would have published these books--he was Maxwell Perkins of Scribner's, you know. And I tell myself that no reputable publisher would. I am puzzled what it tells us about ourselves."

He finds it "amazing" that Charles W. Colson, special counsel to Nixon and born-again prison reformer, should have been commencement speaker at Wheaton College, while former attorney general Elliot L. Richardson, the Boston Brahmin who heroically refused to fire Cox at Nixon's bidding, hardly figures in the commemorative roundups.

Ruefully, Cox recounts an experience at Tulane University. Through a series of mishaps, he found himself addressing 25 embarrassed students in a hall that had been packed to the walls a few weeks before to hear G. Gordon Liddy, the rat-eating, pistol-packing, tight-lipped "plumber" who served the longest jail sentence of them all.

"That is the one that worries me most," Cox said. "I asked what the fascination was for young people--did they want to hear a rebel? But I was told that he is pursuing the right course."