The temperature has reached a point that threatens health and peace of mind. Yesterday was the warmest since roughly this time last year, and we can't promise you that there won't be more of it. The best that we can do for our readers is to offer them this year's updated list of hot weather tips, in the hop that they will survive another dreadful Washington summer with their serenity and their spirits unimpaired.

First, avoid all types of exercise that risk heat stroke -- like the excercise of calculating the actual effects of the Reagan tax bill on your actual taxes. Stick to cooling thoughts, like that thought that your taxes will at least be lower with the Reagan bill than without it. Avoid strenuous work with pencil and calculator, since it will only remind you that the coming reductions in tax rates won't be quite big enough to offset inflation, and, for all but the most fortunate, taxes will continue to take larger shares of income.

Second, try not to think about the bail-outs and giveaways that Congress it tying onto the Reagan tax bill. Thinking about bail-outs is contra-indicated when the temperature is about 90 degrees. In particular, do not think about the savings-and-loan rescue known as the All Savers amendment.It's terrible legislation, and Congress loves it. It will cost taxpayers several billion dollars a year for no public purpose whatever; its sole reason it to rescue some private businesses that are in trouble. Save that one for a cool day.

Third, defer your consideration of the solvency of the Social Security system in the year 20l0. The long-term strain on the system is not quite so severe as the administration's comments might have led you to think, nor is the need to cut benefits quite so urgent. You can safely postpone this one until after the first frost -- this year or even next year.

Above all, abstain from unanswerable questions. They can only raise body heat, inducing perspiration, dizziness and an unpleasant sense of disorientation. Do not try to explain why the interest rates are so high. Do not repond to questions about productivity and whether it will respond to the tonic of the Reagan program. Nobody knows.

Don't ask why the Democrats are turning themselves inside out to match the administration, dollar for dollar, in cutting corporation taxes to the vanishing point. Don't ask why the Democratic opposition to the whole Reagan tax and budget plan has collapsed. Nobody knows the answer to those questions, either.

Drink plenty of liquids, and walk on the shady side of the street. Stop reading books that claim the world economy is about to collapse. Turn instead to detective stories, for they bear the hopeful message that, with perserverance, some puzzles can be solved. Remember that not all crises turn into disasters. Remember that, in time, the evenings will turn cooler.