If you ask most people, they will tell you that the changes of the past generation have erased many of the regional differences in the United States and have blunted the sharp moral edges of controversy over public issues. The conventional wisdom is that we are a homogenized society, governed by people of adaptable conscience.

Both those beliefs were sharply challenged this month in the Senate debate over legislation to restrict the federal courts and the Justice Department from using busing as a remedy for proven cases of school segregation.

The final Senate vote on the bill containing the restrictive language was 57-37. Among senators from outside the Old Confederacy, the vote was 34- 36 against the measure. Among the senators from the Confederate states, the vote was 23-1 in favor.

The one southern senator who voted against the bill was Dale Bumpers of Arkansas. Outside his own state, not much was made of the fact. But his action is more than a rebuke to the majority in the Senate, which pushed through this radical and dangerous abridgment of the independence of the judiciary and the Justice Department. It was equally a reprimand to those who tend to see politics as a "go-along-get-along" scramble for the safest perch from which to prepare for the next campaign.

The point is not to elevate Bumpers to political sainthood. He is as fallible in his judgment as anyone else. But he comes from a state that in 1980 voted out of office two other Democrats, President Carter and Gov. Bill Clinton, who were moderates on race issues and opposed to the court-stripping efforts. He knew what the risks were in the stand he took in isolating himself from every other southern senator of both parties, including his own colleague, David H. Pryor.

This is what he said in explaining his stand: "My words here this morning will not change a single vote. I rise to speak on this issue because I do not want either my children or my constituents to think I acquiesced in or only mildly objected to what we are about to do here. I want them and any person within earshot or whoever may read my words to know that the beginning of the end of constitutional guarantees in this nation occurred over my strenuous and vehement protest."

The essence of his argument was the same one made by the American Bar Association, the chief justices of the state supreme courts, Sen. Barry M. Goldwater (R-Ariz.) and other conservative individuals and institutions, who were prepared to risk offending popular prejudices in order to protect the Constitution.

The argument was that in barring the Justice Department from seeking busing orders or the courts from issuing them (beyond five miles or 15 minutes' travel time), no matter what the findings about segregation in the school system, the Senate was short- circuiting the Constitution and undercutting the independence of collateral branches of government.

The argument did not prevail in the Senate, and it may not prevail in the House, where pressures are building on the Democratic leadership to permit a vote on a similar measure.

Even writing about Bumpers' stance, two weeks after the fact, might be considered irrelevant, were it not for one other point the senator made.

"Completely aside from my own chagrin, dismay and repugnance over our action today," Bumpers said, "I am equally appalled by the virtual silence of the press, which either does not understand the implications of this action . . . or just has not been paying attention."

The precedent of this law, he pointed out, can easily be used to restrict the federal courts from reviewing libel decisions against the standard of the First Amendment or examining police searches of newspaper premises for possible violation of the Fourth Amendment.

Of course, there was regular coverage of the nine-month effort by Sen. Lowell P. Weicker Jr. (R-Conn.) and a few others to block this legislation. But in journalistic shorthand, it was usually described as a controversy about busing and a liberal-conservative fight. The real constitutional issue was submerged.

In time, I think the South will be glad that one of its senators said what Bumpers said about this assault on the Constitution. And the press will be ashamed that more of us did not.