From Walter Mondale's perspective, the economic slowdown that the economy is going through came too gently and too late: the 2.7 percent rate of growth of the gross national product in the third quarter was a far cry from the boom-like pace of 8.5 percent real growth in the first two quarters of 1984.

But people have plenty of cash to spend -- witness the queues for cars at over- sticker prices. The Conference Board says its Consumer Confidence Index stood at 91.1 for October, compared with 80.2 in October 1980. "Consumers are approaching the Christmas season in high spirits," according to Fabian Linden of the research organization.

Treasury Secretary Donald T. Regan, while rejecting talk of a recession next year, had to admit this week that "the economy is not overly strong" and could use a shot of adrenalin in the form of an easier Federal Reserve monetary policy that would bring interest rates down some more.

In any event, the voters going to the polls on Nov. 6 will perceive an economy in which inflation has come down and promises to stay that way, with interest rates moving down modestly, stores and movie theaters full up, and unemployment (although still too high) well below peaks of two years ago. That's a formula that keeps incumbents in and contenders out.

There are many troubles ahead -- but they're not yet visible. They concern budget and trade deficits, an overvalued dollar that makes it nearly impossible for some American industries to compete abroad, and a banking system creaky enough -- according to Secretary Regan -- to have sprouted 70 failures this year (plus 20 S&L failures). Many of these troubles have a common root: the huge federal budget deficit.

The really critical question is not whether 1985 turns into a recession, as some fea, or is yet another year of expansion, as Mondale advisers Walter Heller and George Perry, among others, think. The significant question is how the occupant of the White House for the next four years will deal with the basic problems that stem from the budget deficit.

If it's Reagan, will he stick adamantly to his campaign promises not to raise taxes? Or will he listen to the centrists in Congress and elsewhere in his administration who are hoping that once he disposes of Mondale, he will reverse gears and acknowledge the need for a tax increase?

Sen. Richard Lugar of Indiana, chairman of the Republican Senatorial Campaign Committee, told a savings and loan convention here this week that after the election, Congress will take strong steps "to formulate a plan" for dealing with the budget problem and will look to the White House for "input." But Lugar, while hinting of a modified Reagan stance, warned that it won't be easy to cut the deficit: every lobby group in Washington can be counted oo try to keep intact the spending programs that favor its members.

There just isn't a simple or pain-free way to handle the deficit problem, as Brookings Research Director Alice M. Rivlin wrote recently in The Brookings Review. The problem can't be managed merely by focusing on budget cuts and praying for high economic growth rates: it will take action on the tax side as well.

Out on the stump for the final week of electioneering, Reagan was still pretending that the deficit would go away without tax increases. He has been able to get away with this deception, so long as the economy was doing well enough to disguise the real underlying problem.

Yet, I am persuaded that the Reagan White House knows that deficits matter. Insiders suggest that Reagan, despite his strong personal antipathy to raising taxes, would have left the door open a crack to the possibility of a last-resort tax increase. But Mondale's bold proposal for a tax increase preempted that issue: Reagan couldn't let it appear that Mondale had forced his hand.

Still, a new fiscal policy is needed for the longer term. Privately, some influential Reagan advisers say flat out that the nation can't afford to have deficits at 4.5 percent or more of GNP. Despite Treasury Secretary Regan's commitment to bring in a "neutral" tax-simplification package next month, a competing internal scenario calls for moving after the election with a tax increase and simplification package designed to cut the deficit by about $150 billion in fiscal 1989. The "up-front," or fiscal 1986 portion, would be about $50 billion.

For this plan to succeed, a lame-duck Reagan administration would have to move quickly and dramatically. To be effective, most observers conclude, he would have to get the job done before the end of June.