For the moment, how to cope With recession is Ronald Reagan?Ûªs biggest problem. The slump this year has brought activity down to a point just, over the levels prevailing three years ago. That?Ûªs stagnation?ÛÓit started with Jimmy Carter?Ûªs endorsement of a tight monetary policy?ÛÓand represents millions of lost jobs and billions of dollars in lost output and federal revenue.</br></br>The housing industry, says Michael Sumichrast, economist for the home builders?Ûª association, is ?ÛÏdecimated,?Û? with starts in October at the lowest level in 15 years. The spill-over effects of what amounts to a deep depression in the construction industry are widespread, including a devastating but little-noted impact on the lumber industry in the Northwest.</br></br>of the President?Ûªs Council of Economic Advisers, now admits that the recession will be neither mild nor brief, but equal to at least the average contraction during the postwar period. Instead of a real growth rate of 4.2 percent in 1982 (a question- able forecast the administration used early in the game?ÛÓremember the ?ÛÏRosy Scenario?Û??), Weidenbaum now admits that the growth rAte will be only 1 percent next year.</br></br>And that rate assumes a smart recovery in the second half of 1982, with ?ÛÏthe worst of the recession . .</br></br>. hopefully behind us as 1982 unfolds.?Û? But the trouble is that once it?Ûªs under way, no one can predict