Senate Democratic Whip Alan Cranston of California says President Reagan has "exploded the myth" that the Republican Party is good for business. That may be true of the general public, but the business community itself still clings as tenaciously as ever to its faith in the GOP.

"By virtually every yardstick," Cranston says, "business is worse off now than when Reagan took office." He cited industrial production sinking to the lowest level in five years, plant utilization dropping to less than 70 percent of capacity, corporate profits down by 28 percent.

He could have added that business failures are running at an annual rate of 23,900, by far the highest in 50 years. Bank failures also are at a record level. Auto production is at the lowest level since 1961; steel production is scraping bottom. Also housing starts, airlines, chemicals, mining and metals, are down, down, down.

It might be assumed that by this time the business world would have become disillusioned with Reaganomics and ready to look elsewhere for relief.

But that's not the way it is. While there has been a little private grumbling in the executive suites, our business leaders have almost uniformly shrunk from any public criticism of the Reagan administration. All the signs are that the nation's businessmen, both small and big, will vote Republican as a bloc when they go to the polls Nov. 2.

Actually, there is nothing new about this. It has been going on consistently since Civil War days. Not even the disastrous administration of Herbert Hoover, which triggered the Great Depression and almost wrecked United States private enterprise, alienated the business community.

Hoover, like Reagan today, kept seeing prosperity just round the corner, and called on his business followers to "stay the course." And they did, even as the entire banking system collapsed. They even supported him for reelection against Franklin D. Roosevelt, the president who put the banks back in business.

This extraordinary fidelity to the GOP, for better for worse, for richer for poorer, in sickness and health, through depressions and recessions, is one of the great anomalies of American politics. It has no counterpart among other voting groups.

It might be thought that blue-collar workers would be equally loyal to the pro-labor Democratic Party, but in fact they have not hesitated to defect from time to time, as they did in 1980, when many voted for Reagan.

To some degree, this is also true of blacks and other minority groups who, in spite of being identified with the Democratic Party, have on occasion given Republicans a substantial share of their votes. Dwight Eisenhower, in fact, got about 35 percent of the black votes.

According to the head of the Gallup polling organization, "corporate business leaders remain the firmest bloc in Reagan's constituency." Ninety percent of the executives expressed "confidence in the president's approach to the economy."

Wayne Valis, special assistant to the president for liaison with business, was recently asked if he had been requesting expressions of support from business. "That's sort of like asking the grass to grow," he replied. "You don't have to."

Valis was not exaggerating. The U.S. Chamber of Commerce has just announced its recommedations for the investment of business political action money in the congressional elections. It favors 100 Republicans, no Democrats.

Republican campaign committees have raised nearly eight times more money for the Nov. 2 election than the Democrats have. Even special interests that have been badly hurt by Reaganomics are doing their best to help Republicans defeat Democrats.

The latest Heller-Roper Barometer reports that most small business executives feel that "the interests of the nation and small business would be best served if the Republicans were to win control of both houses of Congress."

Sen. Pete Domenici (R-N.M.) acknowledges that business leaders are wary of telling Reagan of their misgivings about his budget. "Those out there in the business world," he says, "ought to talk more frankly to the president." Sen. Ernest Hollings (D-S.C.) the ranking member of the Budget Committee, says of the business leaders, "They come to us and say, 'no, no, no.' and then see the president and say, 'yes, yes, yes.'"

Sen. Rudy Boschwitz (R-Minn.) has an explanation for this. "When business leaders come into the presence of the president," he says, "they're awed. They don't want to make the president feel bad."