It will hardly shock Reagan-watchers to learn that Lou Cannon's new book about him--as fine a book on American politics as we've had in years--brings good news and bad.

Reagan, as The Washington Post's Cannon portrays him, is an appealing human being with some absolutely appalling work habits.

Cannon likes and respects Reagan, and has followed his political career with beagle's nose and eye since California days. He confirms (it is hardly a secret) that Reagan isn't a detail man and operates a "delegated presidency."

A president may safely delegate much of the busywork that passes for serious public business. But some decisions, affecting the nation's supreme interests, no president can delegate safely.

That is why I am appalled -- no weaker word will do -- at one of the episodes of policy-making described by Cannon: appalled by what it says about Reagan's work habits; appalled by the political double standard to which it unmistakably points.

Cannon's tale, in brief, is this. After identifying himself with the complaint, widely heard in and before the 1980 election, that previous presidents had frittered away the U.S. strategic military advantage, Reagan nonetheless delegated a crucial decision on strategic weapons to Defense Secretary Caspar Weinberger and other deputies who were disinclined to master the details.

The decision was how to deploy the so-called "experimental missile," MX, that was to eliminate the alleged U.S. vulnerability to a surprise first-strike nuclear attack by the Soviet Union.

Cannon, relying on confidential sources, tells us that Weinberger assumed that Reagan wanted at all odds not to offend Western friends by pressing "race track" deployment of MX in the Southwest. (The Carter administration had plans, later abandoned, for a circular underground rail-linked system.)

Weinberger proceeded. He declined to give the Air Force, which wanted the deceptive basing mode, a full hearing. He pushed an unworkable scheme for airborne deployment, though a study had shown MX couldn't be air-launched without blowing the wings off the delivery plane.

Finally, he came up with a plan to deploy MX in old missile silos that had been "hardened," though the experts said they couldn't be sufficiently reinforced to do the job. Reagan approved this plan without study, after Weinberger showed him a cartoon making fun of the problem. "Reagan chuckled and approved," writes Cannon.

That decision also failed to stick. At this writing, the issue remains unresolved. Meanwhile, the supposed "window of vulnerability" widens.

Or does it? The celebrated "window of vulnerability" has never seemed to me quite as plausible a menace as it seemed to Reagan and his most vociferous defense thinkers.

It is strange, however, that those who two years ago professed to be most alarmed by the deterioration of the strategic balance, who crucified Jimmy Carter for canceling the B1 bomber and for negotiating SALT II, have hardly murmured against Reagan's almost frivolous handling of MX deployment.

The record shows that Carter before him had mastered the issue, responded to the worries of his Defense Department and made a politically difficult decision to deploy MX. If the heavy missile is as crucial to the nation's safety and strategic credibility as Reagan and his backers once claimed, why is their bungling of the deployment problem passed over in silence?

Has Reagan discovered, as John F. Kennedy did in the case of an earlier "missile gap," that it was a false alarm? If so, the president should confess. He shouldn't continue to insist, as he does now, that the Soviet Union has a strategic edge.

If, as I doubt, we are now even more vulnerable to a Soviet nuclear first strike, why do we hear no squawks nowadays from the hawks' nests where two years ago that was a favorite theme in the vilification of Carter?

Is it because they believe throwing bales of money at defense problems is a satisfactory substitute for careful presidential judgment? Or do they console themselves with the thought, "What is strategic danger among political friends?"

I am reluctant to think so. But that's the way it looks.