The next Congress

The presidential race all but overwhelms elections for other offices in national attention. But voters should consider that their ballot matters all the way down the ticket in setting their country's policies and direction.

Certainly this is true of Congress. The outcome of the House and Senate races will very much determine the tone and decisions of the 99th Congress - on everything from tax reform and deficit cutting to immigration legislation. Slighting attention to the legislative races is to watch only half of the Washington tennis match.

Congress is still fair game for a certain pop cynicism. Every other year congressional mailings to constituents bulge by some 25 percent - a tidal pattern keyed to reelection, as the 1984-85 edition of ''Vital Statistics on Congress'' shows. Since World War II, in an odd inversion, the number of bills enacted by each Congress has been cut in half, while the number of pages per bill has doubled. Both Ronald Reagan in 1980 and Jimmy Carter in 1976 ran as Washington outsiders, taking advantage of the popular view that Congress's basic instincts are for excessive spending and self-preservation.

But the congressional elections, especially in the House, deserve a closer look in 1984.

If there are 10 or a dozen new Republican faces in the House next January, that will be one thing: The new Congress will be pretty much the current Congress. But if there are 25 or 30 new GOP faces, it could mean something quite different: The aggressive GOP contingent in the House - the so-called ''opportunity society'' group that is banking on economic growth to shrink the federal deficit and who are restless to take more governmental shackles off the individual and the economy - would be further emboldened. This group could frustrate the more pragmatic Republican leadership in the Senate, which would again likely reflect a more moderate, mainstream economic approach.

On the Democratic side in the House, there doesn't appear to be as much action, except in a few key races. There could be as few as 10 or 15 new Democrats in the House. Of the 25 seats in the Nov. 6 contests in which the incumbent is not seeking reelection (incumbents are running in the remaining 410 ), 12 are in Democratic districts. The most watched race is the effort of Budget Committee chairman Jim Jones to hold his Oklahoma seat: If Democrat Jones, considered a moderate, survives in a state that President Reagan is expected to win handily, it could encourage his colleagues in the next session; if he loses, the effect on Democrats, especially Southern Democrats, could be chilling.

Southern Democrats in 1981, together with unusual party-line voting among Republicans, gave the President his winning margin. After that the conservative coalition lapsed. The longer-range trend for Southern Democrats has been toward greater party loyality on key votes, as regional differences on national issues lessen. The election will show whether or not this trend continues.

For the Senate, key races like the bitter Jesse Helms-James Hunt match in North Carolina, reflecting two traditions in Southern politics, and the Charles Percy-Paul Simon contest in Illinois, over control of moderate-state turf, could also indicate emerging trends.

Many of the stronger potential Democratic candidates, sensing that 1984 offered risks because of the improving economy and the incumbent President's popularity, are looking ahead to 1986 as a more promising Democratic year. So this year's outcome may not prove a fair test of the field.

Walter Mondale's debate performances have encouraged Democratic candidates nationwide to step closer to the national ticket. A Mondale victory would surprise them, but the prospects of substantial GOP gains in House seats have been decidedly reduced.

Still, the GOP congressional candidates have been running a generic national campaign - partly on the Reagan record and on the theme of no new taxes. The margin of GOP success could heavily influence what Congress perceives as its mandate for economic policy.