Civil defense plan adds to nuclear war debate

President Reagan wants to increase this year's civil defense budget from $117 million to $252 million to let the Soviet Union know we are prepared for all emergencies.

Another school scoffs at the idea that there is a defense against nuclear attack. It argues that there is no such thing as a ''limited'' nuclear war; there would be no survivors.

''One must conclude that a full-scale nuclear holocaust must lead to the extinction of mankind,'' says Jonathan Schell in a three-part series in The New Yorker magazine.

The Federal Emergency Management Agency (FEMA) has issued some 30 million neatly printed, blue-covered, 98-page handbooks ''In Time of Emergency,'' giving advice for nuclear or other disasters. It offers 10 columns for newspapers that ''could be quickly disseminated at a crisis-building period as emergency guidance.'' These tells how to build fallout shelters, how to interpret warning sirens, and what to take to shelters.

As for pets, ''Leave them home, preferably in the basement, with a two-week supply of water and food,'' the handbook counsels. The tone of the advice is calm and matter of fact: ''Despite continuing efforts to achieve and maintain peace, nuclear attack upon the United States remains a distinct possibility. . . . Undoubtedly millions of Americans would die if a nuclear attack should occur, '' it says. ''However studies show that tens of millions would survive the limited effects of blast and heat.''

Mr. Reagan has decided to almost double spending for civil defense and plans include evacuation of up to 380 ''high risk areas'' in an exercise called ''crisis relocation.'' Plattsburgh, N.Y., has been picked as an experimental area for evacuation.

West Europeans watch US moves with interest and compare them to plans reported from the Soviet Union. At home, Newsweek magazine says that fallout shelters are ''making a comeback.''

A fundamental debate seems to be developing. In his New Yorker articles, free-lance writer Schell argues that there can be no ''limited'' nuclear exchange and that so-called ''deterrence'' won't work. A nuclear attack involving warheads with combined yields of several thousand megatons will annihilate any country many times over, he argues.

Robert McNamara, secretary of defense for seven years under Presidents Kennedy and Johnson, defined this policy: ''Assured destruction is the very essence of the whole deterrence concept. . . . A potential aggressor must believe that our assured-destruction capability is in fact actual, and that our will to use it in retaliation to an attack is in fact unwavering.''

President Reagan and FEMA are asking for increased funds for civil defense partly in the desire to express implacable US determination to stand up to any Soviet threat.

The bomb that demolished Hiroshima was small by comparison with today's nuclear weapons. On Aug. 6, 1945, the US dropped an atomic bomb that had the explosive force of 121/2 kilotons - 12,500 tons - of TNT. That bomb ruined a city of 350,000 in a few seconds with an estimated 130,000 fatalities.

Today bombs are measured in megatons (millions of tons of TNT) not kilotons. The world now has some 20,000 megatons of nuclear explosive power with more being added.

Thus while FEMA is telling householders what to do with their pets in time of possible nuclear attack, another school of thought, summarized by Mr. Schell, is saying, ''We have entered into the zone of uncertainty, which is to say the risk of extinction.''