Most people, says Democratic pollster Peter D. Hart, want to cast "a positive vote" in November, a vote that expresses their hopes for an improving economy - not their fears of even harder times ahead.

That's understandable. On this opening Sunday of the NFL season, even us poor Redskins fans are allowed to hope. But it's interesting to hear a Democratic strategist say what Hart did, because it illuminates the problem -- and the paradox -- the Democrats face in this election.

By some historical standards, the 1982 victory ought to come gift-wrapped to the Democrats, with a card reading, "Compliments of Ronald Reagan and the Republican Recession."

The historical precedents appear awesome. As conservative political analyst Kevin Phillips has pointed out, "The last time the mid-term elections were fought with autumn unemployment at 7 percent or over -- in 1958 -- the GOP lost almost 50 seats." Unemployment now is 9.8 percent. "And," notes Phillips, "the last time that mid-term elections took place with unemployment over 10 percent -- in 1938 -- the Democrats lost 70 House seats."

Those historical precedents explain why people who use economic-political models, like Yale political scientist Edward Tufte, are predicting a 40-seat GOP loss in November. 2 But those precedents are under what you might call unprecedented challenge this year. Phillips himself is skeptical of any such Democratic sweep, and he has lots of company among politicians and political reporters. It can be pointed out, for example, that the heavy losses Phillips noted came in the sixth year of the presidencies of Dwight D. Eisenhower and Franklin D. Roosevelt. Those sixth-year elections are often very tough for the party in power, and not just because of unemployment.

In 1966, six years after the Democrats took over the White House, they lost 48 House seats -- not to unemployment but to inflation and Vietnam. In 1974, six years after the Republicans regained the presidency, they lost 48 seats -- largely because of Watergate.

On the other hand, the first mid-term election after a change of party control of the presidency is often a piece of cake politically for those in power. The Republicans under Dwight D. Eisenhower lost only 18 seats in 1954; the Democrats under John F. Kennedy lost only five seats in 1962; the Republicans under Richard M. Nixon lost only 12 seats in 1970; and the Democrats under Jimmy Carter lost only 16 seats in 1978. Going back a bit further, the Democrats under FDR actually added nine House seats in 1934 -- even though unemployment was far worse than it is today.

The pattern could hardly be clearer: in the last four elections held two years after a change of party control of the presidency, the average loss has been 13 House seats. In the last four elections held six years after such a change, the average loss has been 53 seats.

That says something important about voter psychology. Less than two years into a new president's term, voters tend to be charitable in their judgments. Or, at least, they seem to want to avoid repudiating their own wisdom in putting the new man and his party in power.

That plainly does not mean that a new president has blank-check immunity from repudiation at the polls, no matter how grim conditions may be. Herbert Hoover saw the Republicans drop 53 seats in the first mid-term election after he took office--but the stock market crash that crippled him came in the ninth year of his party's reign.

History seems to suggest that there is some element deeply imbedded in public consciousness that provides fertile ground for the Republican campaign plea to "give the Reagan program a chance." I think that is what Peter Hart meant when he said that voters want to cast "a positive vote."

But, as he was quick to point out, there are ways to vote positively -- and still vote Democratic. A committee of the House Democratic Caucus, representing a broad cross-section of the party, put out a manifesto this week hitting the "unfairness" of many Reagan-Republican policies.

A Democrat who is skillful enough to translate that into a message to "give it a chance - but make it fair," would find a strong positive response, according to the Hart polls. Voters, he says, do not want to repudiate Reagan, but they do want his program modified to correct what is widely perceived as its favoritism toward the rich.

But that is somewhat complicated message to deliver when it relates to budget and tax and spending issues. And because so many voters have been "stunned," in Hart's view, by the roller- coaster ride on the Reagan economy, it's hard to get their attention.

The Republicans are keeping it very simple. Their ads say, "We made the right change in '80. And we are staying right with it in '82." In the present climate, hope and simplicity may triumph over skepticism and subtlety.