In his campaign for Congress this fall, John Sharp has called for the resignation of Interior Secretary James G. Watt and criticized President Reagan for his efforts to dilute the Voting Rights Act and give tax exemptions to private, segregated schools.

That may seem like politics as usual, except for one thing. John Sharp is a Republican.

Sharp, a 38-year-old state representative, freely admits that President Reagan is an albatross around his neck in the heavily Democratic, urban district that encompasses Kansas City.

"The Republican party was a dirty word among poor people and minorities before Ronald Reagan," Sharp says. "He's made it worse."

That makes Sharp's task more difficult this fall. But he is committed to the fight for what he believes is a matter of special importance to his party. He fears that if he loses, it will reinforce the conviction of many conservatives that the GOP should be an ideologically pure party that has no room for moderates and liberals even though this is a district where they have better prospects of beating Democrats than do conservatives.

"If I lose this campaign, it will send a signal to . . . [Republican] leaders that, even if they nominate a liberal in a district like this, he's still going to get blown away," he says.

Missouri's 5th District hasn't seen a good congressional race in more than 30 years, for it is the home base of Democratic Rep. Richard Bolling, a commanding figure in the House and the retiring chairman of the House Rules Committee. But this fall there is a contest, to the surprise and delight of national Republicans.

One reason is the district. Because Missouri lost population and a congressional seat, the 5th District has been expanded to take in several Kansas City suburbs and the city of Independence. While still overwhelmingly Democratic, it has added some conservative voters.

The more important reason is race.

The Democratic nominee, 31-year-old state Rep. Alan Wheat, is black in a district where minorities make up about one-quarter of the population. Neither candidate is playing on the race issue, but other local politicians wonder whether the smooth and articulate Wheat will be able to hold the votes of conservative, blue-collar Democrats.

Wheat hopes the election will be a referendum on Bolling's philosophy.

Sharp is using, like Ronald Reagan's "family, work, neighborhood, freedom, peace" of 1980, a simple litany to attract votes. Wheat's message is: "economy, jobs, Wheat, Democrat."

Wheat and Sharp served in the Missouri legislature. Sharp was the most liberal of seven Republicans in his primary, Wheat the most liberal of eight Democrats.

Both compiled records of support for organized labor and often incurred the enmity of the business community, although Wheat's sponsorship of an urban enterprise zone bill brought praise from the local chamber of commerce.

Wheat has strong support of organized labor, although Sharp has been endorsed by the Missouri affiliate of the National Education Association and the Teamsters. Sharp also feels that despite the resources available to him through the Republican party, Wheat has the advantage in Washington assistance.

"He has the incumbent helping him," says Sharp, who also recognizes the problem of getting people to look past labels.

"There are so many poor people and elderly people angry at President Reagan and the Republicans," he says, "that it's hard to get people to listen."