One voter in northeast Kansas has reduced the congressional race here to an intriguing shorthand. "It's Jack Kennedy versus Jerry Ford," he says.

That's stretching it, but the superficial contrasts in this race are indeed striking.

Playing Jack Kennedy is a Hollywood-handsome Democrat named Jim Slattery, 34, a former state representative from Topeka. In the role of Jerry Ford is Morris Kay, 50, former Republican state chairman, former state representative, defeated candidate for governor -- a man who has paid his dues.

The race is too close to call and many politicians say the deciding factor will be whether the voters buy the Republicans' -- and Reagan's -- argument that his policies must still be given a chance to work.

Kay is trying to make it a contest between a liberal Democrat and a mainline Republican, but it's really between a defender of supply-side economics and an advocate of balanced budgets.

Still, Kay has his lines from the Republican National Committee down pat.

"I think most people in this district would prefer to go forward . . . rather than turn the clock back to the policies of the last 30 years," he says.

Asked why he thinks Slattery is a liberal, he replies, "His first vote in Congress will be a vote for House Speaker Tip O'Neill."

Slattery isn't buying into the connection.

"This isn't a race between Tip O'Neill and Ronald Reagan, it's between Jim Slattery and Morris Kay," he told a group of retired federal employees at a VFW hall in Leavenworth.

That says something about the supposedly liberal Slattery, who was raised in the farm community of Good Intent, Kan., which, if you can believe this, is just a mile "east of Eden."

Even with farm prices depressed and national unemployment at 10.1 percent, Slattery is keeping his distance from the national Democratic party. One brochure he is distributing in the rural areas doesn't even mention that Slattery is a Democrat.

In the last decade, the voters of this district, which is the home of 1936 GOP presidential candidate Alf Landon, have displayed a strong streak of independence in selecting their representatives, having sent two moderately liberal Democrats and one conservative Republican to Washington.

The incumbent, Republican Rep. Jim Jeffries, was elected in 1978 when he defeated former Rep. Martha Keys, whose divorce and remarriage to Rep. Andy Jacobs of Indiana irritated the folks here. But with his popularity slipping, Jeffries chose to retire.

Slattery and Kay agree that the economy is the principal issue, but Slattery pays less attention to unemployment than to inflation and budget deficits. He would also vote to eliminate the third year of President Reagan's tax cut.

"I'm a classical balance-the-budget person," says the young Democrat. "The government hasn't been responsible. And not just the Democrats. It's Republicans too."

Kay has used party ties to full advantage. President Reagan was here earlier, and his praise for Kay is part of the Republican's television ads. Former president Ford and Agriculture Secretary John R. Block have also been here.

By contrast, Slattery hopes that anger over the economy, grass-roots campaigning and the vote of the students in this heavily collegiate district, will overcome an anticipated financial disadvantage and early organizational problems.

"It's a very close race," says Royal Brown, a Republican legislative candidate in Leavenworth. "It's going to be decided on whether people accept Reagan or not."