The implications of the huge Ronald Reagan-Republican victory will be unfolding over a long period of time, but some basic points were clear even as the final returns were being counted.

What defeated Jimmy Carter and the Democrats was the failure to control the costs of necessities and to demonstrate an ability to protect American lives and interests abroad. A year ago, when the campaign was just beginning, voters saw inflation as a threat to their personal security and viewed the plight of the hostages as a symbol of America's impotence in the world.

Nothing that happened in the last 12 months persuaded them that the dangers to personal freedom or national independence were diminishing under Carter and the Democrats. So when Reagan asked if voters thought they and the country were better off than they had been when the Carter presidency began, the answer was an overwhelming no.

Reagan's definition of the issue was so rooted in the reality of voters' own experiences and perceptions that none of Carter's scare-tactic efforts to shift the focus to the challenger could work. And the Reagan tactic played perfectly into the year-long, multimillion-dollar Republican Party advertising campaign to make voters believe that the source of their discontent was not just four years of Carter but 26 years of Democratic control of Congress.

That unprecedented party effort laid an effective foundation for dozens of individual GOP congressional and senatorial candidates to tell their constituents that "if you're going to throw Jimmy Carter out, you ought to defeat the legislators who supported him." With this approach and the resources provided by the party, the PACs and the issue activists, they tied local Democratic candidates to Carter's fatal coattails.

As a result, the conservative victory could hardly be more complete. The back of the liberal cadre in the Senate has been broken. Five liberal Democrats went down to defeat in 1978; in the spring of 1980, Ted Kennedy was rejected for the Democratic nomination; now seven more liberal senators have been eliminated, along with some of the best-known and most influential of their counterparts in the House.

Except for a few aging traditional liberals, like Speaker of the House Tip O'Neill and Sen. Alan Cranston of California, the Democratic leaders in Congress are moderate-conservatives, like House Majority Leader Jim Wright of Texas and his Senate counterpart, Bob Byrd of West Virginia. President Reagan will find them accommodating on most matters.

As for the younger House Democrats, many are political weather vanes, and they will be eager to adjust to the conservative winds, lest they be swept away when the Republicans go all-out for control of the House in 1982, as they surely will do.

So, for the next two years at least, Reagan and the conservatives in Congress will have things very much their own way. The question for the country is whether they will govern in a broad, expansive spirit or a mean and narrow one.

Reagan projected himself during the campaign as a comfortable, outgoing leader, reaching out for support and seeking to broaden his understanding as he widened his constituency. But historically, he has, as he puts it, set his "feet in concrete" on many divisive issues. And many of the newly elected conservatives in Congress look like grim apostles of the right-wing version of revealed truth, who view any dissent as heresy.

The atmosphere in Washington may be like London under Cromwell, when, as the doggerel goes, people said, "England's governed by Objectors. Lord protect us from Protectors."

The first tests of the Republicans' tolerance will be internal. Will the GOP senators keep Howard H. Baker Jr. of Tennessee as their leader, or will they purge him for his "crimes of moderation," as they blackballed him for a place on the national ticket?

Will Reagan insist that places on his White House staff and in his administration be open to all Republicans and to "discerning Democrats," or will he permit the ideologues who have a long investment in his career to bar access to everyone but their philosophical clones?

Those are the earliest clues the country will get about what kind of people it has voted into power. But the most important test -- in my view -- will lie in what Reagan and the victorious conservatives do to reassure worried black and brown Americans about the implications of their victory.

Carter was accused of demagoguery when he said a Reagan victory might separate the races in America. But, in fact, that separation occurred in the voting booths last Tuesday, as blacks and browns, almost alone, gave their support to Carter in overwhelming numbers.

Many in the minority communities are frightened by their isolation from their partners in the old New Deal coalition and by the fact that the victorious conservatives owe them nothing politically. There is little they find reassuring in Reagan's past pronouncements on civil rights laws and social welfare issues.

Dealing with those fears will be the work of many years, but it can begin by including strong black and brown leaders in the planning and staffing of the new government. Nothing would contribute more to letting Reagan launch this new conservative era on the right note.