You don't have to be here long to know a lively political campaign is in progress. On the drive in from the airport, you pass platoons of yard signs advertising the rival candidates for the House: state Sen. John Kerry (D) and former state Rep. John McKernan (R). The rivals for the seat being vacated by Rep. David F. Emery (R), who is challenging Sen. George Mitchell (D), are both able and attractive men, debating with gusto issues from the balanced- budget amendment to the nuclear-weapons freeze.

It's the kind of campaign you would like to see in every district, but it is, in fact, a rarity. Probably less than one-fifth of the House districts are enjoying adequately financed races between Democrats and Republicans who have the personal and organizational skills to make their contests competitive. That fact clouds the predictions of virtually every national polling organization that the Democrats will gain 30 seats or more in next month's election. A 30-seat gain doesn't sound like much in the 435-seat House. But when you realize that the Democrats must win two-thirds of the 90 or so really competitive districts to make a gain of that size, you realize it's a lot tougher than it seems.

The best description of this paradox was written by Alan Ehrenhalt, the political editor of Congressional Quarterly, in his introduction to CQ's detailed survey of the 1982 election contests, published this week. "The Nov. 2 congressional election," he wrote, "is like a trick portrait that changes shape and context as one approaches to examine it. Seen from a distance, this is a national referendum on a stagnant economy, massive unemployment and the Republican administration presiding over those problems. Up close, though, it is a collection of individual campaigns in which strong and well- financed Republican candidates seem to be overriding any urge the electorate might have to punish the party in power. A month before Election Day, it is still plausible to argue that Democrats will gain 30 or more House seats. . . . But weeks of checking and rechecking . . . offers scarcely any clue to just where those vulnerable Republicans might be."

I have been struggling with the same question myself. In the last three weeks, crisscrossing the country, it has become evident that the election has been sliding in the Democrats' direction. Emboldened by economic adversity, Democrats have begun to attack the fundamental premise of the GOP campaign: that if voters just renew President Reagan's mandate by supporting Republican candidates, everything will work out all right.

The Republicans' own polls are telling them the Democrats are gaining ground on the unemployment issue. That is why they are putting their best spokesman, the president, on TV tonight. The speech he is making on the economy is their last best hope to redefine the major issue in terms that will bolster their candidates, by emphasizing the progress that has been made on inflation and interest rates. If it fails, the Democratic trend will probably gather momentum in the 20 days remaining.

But as of now, the Democratic prospects are spotty -- not solid. In the last 10 days, I have talked with Democratic congressional candidates in Salem, Ore., Savannah, Ga., and here. These races would be on anyone's target list of key contests. But when I saw them, none of the three had received any direct financial contribution from the Democratic Congressional Campaign Committee. The quality of their own improvised campaigns ranged from artful to awful.

Ehrenhalt, I think, has it right when he says that "if this year produces a Democratic landslide, it will be one of the latest-breaking landslides in modern times." It sure isn't here yet. ch of The Landslide By David S. Broder

PORTLAND, Maine--You don't have to be here long to know a lively political campaign is in progress. On the drive in from the airport, you pass platoons of yard signs advertising the rival candidates for the House: state Sen. John Kerry (D) and former state Rep. John McKernan (R). The rivals for the seat being vacated by Rep. David F. Emery (R), who is challenging Sen. George Mitchell (D), are both able and attractive men, debating with gusto issues from the balanced- budget amendment to the nuclear-weapons freeze.

It's the kind of campaign you would like to see in every district, but it is, in fact, a rarity. Probably less than one-fifth of the House districts are enjoying adequately financed races between Democrats and Republicans who have the personal and organizational skills to make their contests competitive. That fact clouds the predictions of virtually every national polling organization that the Democrats will gain 30 seats or more in next month's election. A 30-seat gain doesn't sound like much in the 435-seat House. But when you realize that the Democrats must win two-thirds of the 90 or so really competitive districts to make a gain of that size, you realize it's a lot tougher than it seems.

The best description of this paradox was written by Alan Ehrenhalt, the political editor of Congressional Quarterly, in his introduction to CQ's detailed survey of the 1982 election contests, published this week. "The Nov. 2 congressional election," he wrote, "is like a trick portrait that changes shape and context as one approaches to examine it. Seen from a distance, this is a national referendum on a stagnant economy, massive unemployment and the Republican administration presiding over those problems. Up close, though, it is a collection of individual campaigns in which strong and well- financed Republican candidates seem to be overriding any urge the electorate might have to punish the party in power. A month before Election Day, it is still plausible to argue that Democrats will gain 30 or more House seats. . . . But weeks of checking and rechecking . . . offers scarcely any clue to just where those vulnerable Republicans might be."

I have been struggling with the same question myself. In the last three weeks, crisscrossing the country, it has become evident that the election has been sliding in the Democrats' direction. Emboldened by economic adversity, Democrats have begun to attack the fundamental premise of the GOP campaign: that if voters just renew President Reagan's mandate by supporting Republican candidates, everything will work out all right.

The Republicans' own polls are telling them the Democrats are gaining ground on the unemployment issue. That is why they are putting their best spokesman, the president, on TV tonight. The speech he is making on the economy is their last best hope to redefine the major issue in terms that will bolster their candidates, by emphasizing the progress that has been made on inflation and interest rates. If it fails, the Democratic trend will probably gather momentum in the 20 days remaining.

But as of now, the Democratic prospects are spotty --not solid. In the last 10 days, I have talked with Democratic congressional candidates in Salem, Ore., Savannah, Ga., and here. These races would be on anyone's target list of key contests. But when I saw them, none of the three had received any direct financial contribution from the Democratic Congressional Campaign Committee. The quality of their own improvised campaigns ranged from artful to awful.

Ehrenhalt, I think, has it right when he says that "if this year produces a Democratic landslide, it will be one of the latest-breaking landslides in modern times." It sure isn't here yet.