In an astonishing passage tacked on to his otherwise routine effort to sell his defense budget by puffing the competition, President Reagan has called on American scientists to join in a mighty effort to develop an effective defense against nuclear missiles. He reminded us that it was the scientists who gave us the bomb in the first place, and this reminder invites a look at the way an earlier president made the decision then to join that effort.

Franklin Roosevelt's basic decision that the country should get a bomb if it could was made on Oct. 9, 1941 (not in 1939 when Einstein wrote his famous letter; the net effect of that letter was probably to slow things up.) The decision was made in immediate response to a firm and clear recommendation from Vannevar Bush, a scientific administrator of the first order. Bush's recommendation was the product of a review process that he had shared with his colleague James B. Conant.

They were moved primarily by the extraordinary Maud Report of British scientists, which had reached the firm conclusion that a wartime bomb was indeed possible. The Maud Report in turn was the product of a year-long review triggered by a brilliant secret memorandum of early 1940 in which the refugee scientists Frisch and Peierls had been the first to report the probability that very small amounts of separated U-235-- the more readily explosive isotopes of uranium--could make a very big bang.

Roosevelt's decision, which led not to a speech but to action, was the product of extraordinary discoveries by extraordinary men of science and careful, initially skeptical review by men in two countries whose capacity for judging scientific questions had been professionally tested at the highest levels. The lonely and enormous decision was indeed made by the president, but in a very deep sense he did not call on the scientists for action until what they had learned led them to call on him.

Compare this process of decision to Reagan's. Does his proposal rest on any new scientific insights? His advisers have told the press it does not, and scientists of the first rank, with access to all our present secrets, confirm the absence of any new idea remotely comparable to that of Frisch's and Peierl's. Was the decision the product of any analysis and review even distantly resembling the work of the Maud Committee or the examination by Bush and Conant? Clearly not. It appears to be a quick-trigger personal response to the frustration of military advisers, some of whom do indeed devoutly wish they had a good way to defend the increasingly implausible MX missile.

Was there any serious consultation at all with experts and leaders in the scientific community? Apparently not. Reagan wanted a news-making speech more than he wanted a good decision, so consultation was tightly limited both in scope and in content. The first major gathering of eminent scientists took place only after the speech had been handed out to the press. At this meeting, which also included a number ex-officials from earlier administrations, the president was a most generous and gracious host, but it was not a meeting in which serious advice

could be sought or offered; its

formal proceedings lasted only

45 minutes. The decision-

making processes of the two

presidents could hardly be

more different.

The realities of the two

decisions are just as far apart.

Roosevelt's decision led to

rapid and awesome results.

Reagan's will not. He himself,

warned by his advisers, has

made it clear that serious re sults may not be achievable in

this century, and he has ex plicitly affirmed his continuing

allegiance to the ABM Treaty,

which forbids the very action

he sets as a distant goal. The

immediate result of the speech

is minimal: an instruction to

the Joint Chiefs to see if they

can find better ways to do

what they are doing already

with about a billion dollars a

year. Research work on defense against missiles is a prudent form of reconnaissance that is permitted under the ABM Treaty. Like most human activities, it probably can be done better than it now is, quite possibly for less money.

Everyone who has ever worked in the White House knows how the desire to pump up a speech can get in the way of sober second thought. But it is important in such cases for the rest of us not to mistake that normal impulse for serious and substantial change in policy. If our leading men of science could in fact see a good way to put the defense truly ahead of the offense in strategic weapons, we would indeed have a great choice to make. But they don't, and so we don't. Let the research effort continue; let the Defense and Energy departments improve it if they can; and let us all relax a bit, starting perhaps at the top.