WASECA, MINN. -- George Bush is getting his campaign into gear in the nick of time. The Republican opposition is warmed up and ready to play -- at least for laughs.

The other afternoon here, Jack Kemp stood flat-footed at a podium in Waseca High School's cavernous gym, grabbed a football and tossed a long, looping spiral pass into the hands of the Blue Jays' crew-cut flanker, standing behind the last row of folding chairs. Kemp told the cheering fans he'd learned it from his son Jimmy, ''who plays for Winston Churchill High School in Bethesda, Md. . . . (pause) . . . Well, you didn't think a son of mine would play for Neville Chamberlain, did you?''

Four days earlier, Bob Dole faced 50 Keene, N.H., Republicans, invited to a continental breakfast and get-acquainted session in Henry David's restaurant. ''I wish Elizabeth were here today to meet you,'' he said, ''but she's down in South Carolina. She's a great asset to the campaign. . . (pause) . . . because she speaks Southern fluently.''

Neither of these lines is likely to make it into Mark Shields' Anthology of Great Political Humor. But in a year of sparse wit, they aren't bad.

And these are not bad candidates, these two men who most party insiders regard as the principal challengers Bush must overcome in the campaign he formally announces tomorrow. Over the summer months, when most of the attention was focused on the shenanigans in the Democratic field, Dole and Kemp learned their lines pretty well and became more adept in delivering them.

For Dole, the most obvious difference is his willingness to let people see a bit more of the personal experiences that have shaped his life. Behind the polished and power-wielding Senate leader who snaps off shorthand comments about the issues on the legislative agenda, he is letting audiences discover a man who has known some searing personal moments.

It is a selective, sometimes sentimental, autobiography: the father who ''worked in overalls for 42 years and was proud of it,'' the mother who sold sewing machines and gave sewing lessons; the young athlete grievously wounded in the war who spent 39 months in and out of hospitals, his treatments subsidized by caring home-town friends; the young county attorney who found his grandparents' names on the welfare list each month, ''not because they were lazy but because they were poor,'' and who never has forgotten that those in need through no fault of their own have to know the government will help them.

It's an affecting tale, as Dole tells it, and it softens the image of a man whose past appearances in the national spotlight -- especially during his 1976 run as the vice presidential nominee -- left an impression even among fellow Republicans of a hard, even harsh, personality.

If Dole is more generous in the view he offers of himself, he is still skimpy in sketching a picture of his possible presidency. He identifies the budget deficit as ''public enemy No. 1" and ''my top priority'' as president. He says that he put together an effective proposal for dealing with it in 1985 and got it through the Senate by one vote, only to watch in frustration as ''the White House pulled the plug on me.''

But he's skimpy on details of what he proposes to do now on the deficit and is almost mute about his larger agenda for the government and the nation.

Kemp, on the other hand, is both specific in his proposals and large-minded in his vision of his party and his presidency. But unlike Dole, who conveys a sense that his whole life has steeled him to accomplish his objectives, Kemp leaves some in his audiences wondering how much of what he says is ''just talk.''

The vision is glittering: an America made secure against nuclear attack by deployment of a strategic defense system and leading a worldwide revolutionary movement for freedom; this nation supporting freedom fighters against repressive regimes of the left and the right, while building international markets untrammeled by trade barriers, and enjoying low taxes that encourage entrepreneurship even in the ghettos and barrios, the blighted cities and the depressed rural areas.

Is all this beyond the reach of a retired quarterback and minority party House member from upstate New York? Common sense says yes, but then one remembers this is the same mind that conceived a radical reduction in personal and corporate tax rates and the same relentless energy that pushed that idea into law.

Neither of these men enjoys Bush's enormous advantages among Republicans as Ronald Reagan's chosen partner in two elections and two administrations. But watching them, they seem ready to test Bush's claim to the nomination -- and to ensure that whoever carries the Republican banner in the general election will be toughened for the battle.