POLITICS / UNOPPOSED CANDIDATES : Many in Congress Lack Challenge : The number of uncontested elections is growing. The belief is that seated lawmakers are unbeatable.

From coast to coast, congressional elections are increasingly becoming a game of solitaire.

Already, 75 U.S. representatives are guaranteed no major party opposition in this fall’s election. By the time filing deadlines in all the states close, that number could reach into the mid-80s, up from 47 a decade ago. Likewise, four senators have drawn no major party challenger.

VOTERS STYMIED: In a year when disenchantment over the savings and loan scandal and deadlock over the budget have produced glimmers of resentment against incumbents, that means voters will have no chance to register their feelings for perhaps nearly one-fifth of the House members and about one-eighth of the senators on the ballot this year.

“There are very, very few challengers, and yet the atmosphere is such that you can take some of these guys out,” lamented Charles E. Cook, the publisher of a political newsletter in Washington. “As a result, what could be an anti-incumbent year is likely to be so only in isolated circumstances.”

Like the boll weevil, uncontested races once were a uniquely Southern blight, as Republicans routinely chose the better part of valor against entrenched Democratic incumbents. But the pattern has spread. Eight of New York’s representatives are unopposed in the general election. So are five of 11 in Massachusetts, six in Pennsylvania, five in Illinois, three in Wisconsin and two each in California and New Jersey.

Free passes are still a mainstay of Southern politics--but now on a bipartisan basis.

In Virginia, for example, Republicans failed to find challengers for any of the five Democratic House members seeking reelection. But the Democrats could not produce a candidate to oppose Republican Sen. John W. Warner. Republicans found no one willing to step up against powerful Democratic Sens. Sam Nunn in Georgia and David Pryor in Arkansas; but Democrats were unable to recruit an opponent for Republican Sen. Thad Cochran in Mississippi--a state that did not elect its first Republican senator in this century until 1978.

In both Texas and Florida, five Republican representatives are running unopposed--as are 10 Democrats in the two states.

WHY IT’S HAPPENING: Experts cite several reasons for the growing number of races without even token opposition:

The conventional wisdom that it is virtually impossible to unseat an unindicted incumbent with a steady pulse. “These people are being told . . . you cannot win, so they don’t run,” Cook said. “This all becomes terribly self-fulfilling.”

The high cost of campaigning. In Virginia, former Rep. Joseph L. Fisher seriously considered running against Warner but backed away when he decided he could not raise enough money to topple an incumbent. “I doubted I could get enough money together to have a good chance,” he said.

The imminence of congressional redistricting. “You are seeing a lot of (potential) challengers say 1990 is not the best year to run,” said Howard Schloss, communications director at the Democratic Congressional Campaign Committee. “People don’t want to run in a district that is going to disappear in two years.”

The expectation that a large number of incumbents may step down in 1992, the last year, under campaign reform laws, in which retiring members with enough seniority may convert to personal use any campaign surpluses they have accumulated.

The growing tendency of local party leaders to discourage challengers from stirring secure incumbents who, if faced with opposition, might unleash media and field operations that could benefit all the candidates on their ticket.

LARGER IMPLICATIONS: Many analysts consider the rise in uncontested races only the most tangible symbol of a larger problem: the stunning decline in competitive congressional races. In the last election, not only were 98.5% of all House members reelected, but more than 88% of them were sent back to Washington with over 60% of the vote.

This year, analysts estimate that as few as two dozen House members could face serious competition. “It’s bizarre,” said Thomas E. Mann, director of government studies at the Brookings Institution. “The fact is every state in the union ought to be competitive.”