The sound that filled the Opryland Hotel last weekend was not country music but the voices of seven of the Republican presidential hopefuls, trying out their tunes for 1,400 GOP activists from across the South. Here are some first impressions of the performers as they start their auditions for the 1988 primaries.

George Bush -- Draws the leadoff spot at the Southern Republican Leadership Conference and establishes immediately that he is a high-class act. An offstage amplified voice intones, "Ladies and gentlemen, the Vice President of the United States," and a recorded band plays "Ruffles and Flourishes."

He turns over his second trump by reminding them that he has been working for the GOP since "Barbara and I organized the first Republican primary in Midland, Texas, in 1952."

Loyal service to President Reagan and years of party chores are Bush's claim checks for the nomination, and they may be enough. But he reads his speech on aid to the contras in wooden fashion. What will happen if he has to campaign as plain George Bush and not as an extension of the Omnipotent Reagan? Maybe his managers can get him nominated before that happens. If not, watch out.

Howard H. Baker Jr. -- Fifteen months after he retired, the former Senate majority leader looks more rotund and relaxed than ever, two reasons why even some of his home-state Tennessee boosters wonder if he really will run for president again. To counter the skepticism, Baker calls a news conference to introduce a top- notch New Hampshire political pro, former attorney general Tom Rath, as director of his exploratory committee.

If Rath and Sen. Warren Rudman (R-N.H.) can engineer a surprise for Baker in the 1988 New Hampshire primary, he might ride the momentum into the mid-March southern primary and caucuses, where he can play the Good Old Boy. As of now, the odds look as long as his belt.

Pierre S. (Pete) duPont IV -- On paper, he looks like a potential Gary Hart, the hard-working dark horse with a "new generation" theme who might pop into contention when a front-runner fades. But his early- morning speech the second day is a hymn to the virtues of "success in the American marketplace," hardly a theme a duPont needs to drive home. Curiously, he neglects to tell the story of his skill in making supply-side principles work for eight years as governor of Delaware, so the delegates leave knowing little more than that he is an earnest, pleasant fellow.

Alexander M. Haig -- The former White House chief of staff and secretary of state looks every inch a president: silver hair, silver tie, deep tan and a sharp blue blazer. He deflates his reputation for egotism with effective, self-mocking humor and boldly challenges some of Reagan's stands.

He says the doubling of the national debt in the past five years "can't be blamed on Jimmy Carter," that the all- volunteer military won't work forever, and that Reagan was right to accelerate "Star Wars" research but wrong to make it such a high-profile project. Will the GOP nominate someone who was squeezed out of the Reagan administration and occasionally ridicules the party's hero for sleeping overtime? Doubtful.

Pat Robertson -- In a smash debut on the political scene, the TV preacher steals the day's headlines and loudest cheers by attacking Democratic National Chairman Paul G. Kirk Jr.'s knock on evangelical Christians' moving into partisan politics.

Southern Republican leaders covet Robertson's constituency but are skeptical they want him as their candidate. It's notable that, even with this crowd, no other contender hits the "social issues" nearly as hard as Robertson. If they continue to give him that ground for himself, could he carve out a piece of the primary vote? He's an intriguing X-factor.

Robert J. Dole -- The Senate majority leader displays the maddening penchant for put-downs that marred his earlier national campaigns in 1976 and 1980. He boasts that he led the Senate with a 92 percent Reagan support score, but he cannot resist adding, "That means he's wrong only 8 percent of the time."

It would take a psychiatrist to explain why the Kansan, a gifted and often courageous legislator with real convictions, persists in playing the cynic and the clown in public. He does what is easy -- getting laughs -- and avoids what is hard -- explaining why his views on taxes, deficits and civil rights are good policy for the Republicans' future. The audience loves Dole the Entertainer; those who think he might in fact make a president feel cheated.

Jack Kemp -- He may not be the legislator Dole is, but Kemp, like Reagan, understands that what fuels a political party is vision, inspiration, optimism. It is late in the day when the Buffalo congressman speaks, but he has them cheering when he says Republicans have a nobler mission than "defeating Democrats. . . . We can bring the hope of freedom to men and women of every color and culture."

Kemp also shows why he is a high- risk candidate: His mouth sometimes outruns his brain, as when he says of his high-speed circuit of the issues, "Well, I've given you a grand tour de force."

Whether the GOP chase will prove to be just a tour or a tour de force, I don't know. But it isn't starting out dull.