Tell me that Mayor Ed ("While I know it was the people who elected me, it was God who selected me") Koch is actually humble. Tell me that Guru Bhagwan Shree ("So many religions look after the poor, leave the rich to me!") Rajneesh is driving a 1967 Volkswagen beetle to work. But don't tell me, as The New York Times poll does, that 56 percent of American blacks approve of the job Ronald Reagan is doing as president.

That was the popular reaction among some Democrats to the earthquake news that Reagan, who just three years ago in one Republican poll was rated favorably by only 4 percent of the blacks interviewed, was now earning good marks from more than a majority of black Americans.

For every Democratic presidential candidate in the post-civil rights era, black voter support has been the acid test of authenticity. The Democratic candidate without black support was suspect.

In 1976, his ability to win black votes legitimized Georgian Jimmy Carter. In 1984, the Colorado candidate's shortage of black votes was cited as proof that Gary Hart lacked soul.

White Democrats, in requiring national candidates who could win black support, seemed willing to endow black voters with some rare miracle- moral-X-ray gift, a quality that enabled black voters to better judge the character of would-be presidents. Moreover, it seemed only fair to require the Democratic nominee to have some rapport with blacks, who have remained the most loyal Democrats, "the people," in analyst Bill Schneider's phrase, "who are with us when we are wrong."

In the judgment of Republican pollster Bob Teeter, two factors converge to explain the Reagan surge: "The president is an immensely popular figure and the country is in good shape." Teeter recalls the Chicago newspaper headline reporting House passage of the tax bill: "Reagan Wins." Since 1981, an almost mythic-hero quality has developed about Reagan the man. After all, he has survived a speeding bullet and routed, the country sincerely hopes, cancer from his body. He spent the fall seeking peace with the Soviets and tax reform from the Congress, a reform that, in addition to removing 6 million poor Americans from the tax rolls, transfers the tax burden from individuals to corporations.

For both substantive and tactical reasons, Democratic criticism of the president has been mostly missing for the past year. Substantively, the president's 1985 initiatives -- unlike earlier efforts to win tax credits for segregationist Bob Jones University or eliminate child nutrition programs -- have not cast him as The Villain. Tactically, elected Democrats, after losing 93 of 100 states to Reagan in two elections, apparently concluded that steady public criticism of the president was neither hurting him nor helping them. With 1986 legislative carnage over budget cuts guaranteed by the Gramm-Rudman law, the political climate will not remain as chummy.

But even so, few among the Democratic opposition are volunteering to go three rounds with the heavyweight champ. Acknowledging Reagan's popularity, Kennedy strategist Paul Tully detects "no groundswell among Democrats for repeal of the Twenty- Second Amendment," which limits Reagan to two terms. Echoing the mythic-hero analysis, Tully believes Reagan has "moved onto Mount Rushmore," adding that no recently successful political strategies have included an attack on the presidential profiles carved there.

The president is not the only elected executive now winning high marks from his constituents. Govs. Mario Cuomo of New York and Tom Kean of New Jersey and former governor Chuck Robb of Virginia all have comparable ratings in their home states. Reagan may be said to have benefited from the nation's return to a Positive Political Era, an era his own optimism and confidence have done much to encourage. In just three years, the conservative president has de-demonized himself.

Paul Goodman, who last year managed Doug Wilder's successful campaign to become Virginia's first black elected statewide official, sees a lesson for the Democrats in the latest Reagan numbers. "You can't indefinitely sell a negative message in American politics," says Goodman. "Americans -- of every race -- cannot exist without hope."

Not too much should be made of the results from one poll. But wouldn't it be terrific if Republicans began genuinely campaigning in national elections for black votes and no longer pretended the American electorate had the same pigmentation as, say, Sweden's? Such a change would be terrific for both parties and for all voters, black and white.