THE SAME WAY Richard Nixon had to convince Republicans in 1968 that he was not a loser, Nelson Rockefeller, if he wants to be president, must prove by 1976 that he is not a liberal. So far, he is succeeding.

When Rockefeller announced his resignation as Governor of New York last week, conservative Republicans were quick to praise the man they had always loathed.

"Maybe he's changed, maybe the people have changed, but he's totally accepted now," Kansas Sen. Robert Dole said of Rockefeller. "Right now, he's a very viable candidate [for president]."

William Loeb, the frantically right-wing publisher of the Manchester (N.H.) Union Leader, said he was keeping an open mind about Rockefeller, whom he had called "the wife-swapper" in 1964 after Rockefeller's marriage. "He's now a staid old married man," Loeb said last week.

To earn such kudos, Rockefeller has stumped the country in recent weeks as a gravel-voiced Spiro Agnew, bragging about New York's tough new drug law, decrying welfare cheaters, and heaping praise on Republican stalwarts. (In Arizona, he paid effusive tribute to Barry Goldwater. Apparently, ambition heals all wounds.)

IT IS IMPORTANT to remember, though, that Rockefeller is changing merely his image. His politics have always been conservative, although he has managed to pass himself off as a progressive when it suited his needs (such as when he ran against Nixon and Goldwater).

In April 1968, I.F. Stone chronicled Rockefeller's conservatism in his now-defunct Weekly:

Behind Rockefeller's ignominious silence on Vietnam is a more consistently hawkish record than that of any other candidate, except perhaps Nixon. The Rockefeller Brothers report of 1958, in which Nelson played a major role, was an effort to pressure the Eisenhower administration into larger arms expenditures for Pax Americana policies. The Kennedy Administration's boost in arms expenditures, development of "flexible response" for limited wars, and its more belligerent foreign policies all met with Rockefeller's approval, though he did not think Kennedy went far enough. Rockefeller was for a second try at Castro after the Bay of Pigs and he supported the nuclear test agreement reluctantly. He was the country's leading enthusiast for the delusion that there could be civil defense against nuclear war. He was for U.S. intervention in the Congo, where the Rockefellers have extensive interests and as late as March 19, 1967, he was fervent in his support of Johnson in Vietnam.

On the last point, Vietnam, Rockefeller was the consummate politician. Sensing a chance in 1968 to attack Richard Nixon for his phantom "secret plan" to end the war, he and his adviser, Henry A. Kissinger '50, devised a detailed position that Rockefeller could espouse. Their plan was "progressive" in 1968. It called for free elections and a gradual withdrawal of U.S. troops. But it was a devised position, nothing Rocky felt in his gut. Witness a press conference on March 21, 1968, just before he decided to acquire a position on the war:

Q: Governor, could you please outline for us your views on Vietnam?

A: Sure. My position on Vietnam is very simple...I think that our concept as a nation, and that our actions, have not kept pace with the changing conditions. And therefore our actions are not completely relevant today to the realities of the magnitude and the complexity of the problems that we face in this conflict.

Q: Governor, what does that mean?

A: Just what I said.

Q: Governor, you said that your Vietnam policy offers constructive alternatives to President Johnson's [and] to Mr. Nixon's Vietnam policy...

A: Well, I'm not in a position to discuss anybody's policies, frankly...

Q: Governor Rockefeller, should we now cease the bombing of North Vietnam?

A: I'm not prepared to make any tactical suggestion.

ROCKEFELLER's record since 1968 shows more such sleazy conservatism and mindless opportunism.

He is recognized as an "urban" spokesman, but he has accelerated the decay of Manhattan by starving New York City for funds. This he did partly to make potential political rival John Lindsay look bad.

He undertook an extended mission to Latin America for Nixon in 1969. While he courted fascist dictators in their palaces, he was vilified in the streets--and that puzzled him.

He gave the order for state troopers to storm Attica prison. Forty-three men died, most of them prisoners. A Rockefeller-appointed commission later blamed the deaths on police gunfire, but no policeman has yet been indicted--and Rockefeller is not puzzled by that.

He steered a law through the state legislature requiring life sentences without parole for convicted heroin pushers. That hasn't forced them out of business, though; it has merely made their heroin more expensive, which means addicts must now rob more apartments, and mug more old women, to get enough money.

There are, of course, positive sides to Rocky's record. He refused to endorse Goldwater in 1964 even though he suffered intense scorn from party regulars. He signed New York's liberated abortion law, one of the nation's first, and fought attempts to repeal it. He has never been accused of corruption (although that reflects more credit on his family fortune than his scruples).

As Nelson Rockefeller begins his fourth presidential campaign today, it is tempting to laugh him off as a rich man's Harold Stassen. But he is more substantial than that, and therefore more dangerous.

Rockefeller might win the Republican nomination and even the presidency. That he would be better than Richard Nixon means nothing. That he is an ebullient, personable, witty man means nothing.

Above all, Rockefeller is the rigid conservative that he now swears he is. He is not tilting rightward to win the nomination, only to tilt to the left after his election. In places like Arizona and North Dakota, speaking before Republicans who are happy with America and cling to the status quo, Nelson Rockefeller is showing his true colors. Listen to him.