IF YOU ARE AMERICAN, male and will be between 24 and 40 years old on June 30, this book is about you.

It is about how the "Vietnam Generation" responded to that war and how close it came to collapsing the selective service system and snarling the war effort, not because of the draft card burnings of a few but the eagerness to avoid military service of the many.

Of the 26.8 million, 10.9 million served in the military and 2.1 million served in Vietnam. The professionals wanted to go - so much so that not all the graduates of the West Point class of 1966 who asked for Vietnam duty could be accomodated - but, for the most part, the foot soldiering was left to the poor and ill-educated, whose lack of knowledge extended to ways to avoid military service.

Lawrence M. Baskir (who joined the reserves) and William A. Strauss (who got a safe lottery number) document a nation's attempt to fight a war that was unpopular even with millions who in no way considered themselves antiwar. It was personally unpopular: they preferred to go to law school than to Cuchi, Chulai or Dongtam.

Those draft evaders who became symbols of cowardice for Richard Nixon and Spiro Agnew did not do anything fundamentally different, the authors say, from their 24 million peers who avoided the war by legal means.

Student deferments grew by 900 percent between 1951 and 1966. When the Emory University newspaper ran a prank story reporting that student deferments were going to be cancelled for all Emory students, a number of students immediately telephoned transfer applications to other schools.

In 1968, when the New York City draft boards said that full-time teachers qualified for deferments, the board of education received 20,000 more applications than the year before.

"If you've got the dough, you don't have to go," lawyers told would-be legal draft avoiders.

A Samoan conscientious objector applicant got his exemption because of his belief that if he killed anyone his god would cause a volcano to erupt.

"By 1971, the enforcement of the draft law was in shambles," Baskir and Strauss write. They draw a picture of a system so full of loopholes and so inequitable because of differing local draft boards that it tottered on the brink of collapse. In the hope that enough eligibles would docilely line up and go off to war thinking they had no choice, the system tried to conceal its vulnerability from eligible men seeking to beat the draft.

The draft counseling by antiwar organizations and the availability of lawyers who had close to perfect scores in preventing their clients' inductions made the manpower pool going to Vietnam even more heavily minority and poor than it might otherwise have been. A Chicago study found youths from low income neighborhoods three times as likely to die in Vietnam as their peers from wealthier neighborhoods.

The marines and the army had the worst problems, of course, because they did most of the fighting and dying. "People don't seem to enlist in the army to fight," a Pentagon manpower expert confessed to the authors. Moreover, it was well known, as one sailor said, "There ain't no Vietcong submarines." Safety in the service could be found in many ways, as Baskir and Strauss report. "If we had been called up," a reservist in one Philadelphia unit said, "the Eagles would have been left without a backfield."

In 1969-1970 more college-trained men entered the National Guard or Reserves than entered all the active duty branches of the service.

Numbers like that - which abound in this excellent book - and our lack of success in fighting wars without involving more Americans, raise questions about the future and viability of the present volunteer army, which the United States turned to after the failures of the draft for Vietnam. The volunteer army is increasingly black and from low-income groups, according to recent Pentagon reports. It is also an army from which people are checking out with alarming frequency. In fiscal year 1977 almost 30 percent of the new recruits failed to finish two years of service.

Although I find Baskir and Strauss most fascinating in their discussions of the draft and its problems, their book also includes interesting sections on amnesty, exiles and deserters. Unauthorized leaves cost the military one million man-years, almost half the man-years U.S. troops spent in Vietnam.

Chance and Circumstance knocks for a loop the popular image of the deserter as the spoiled, rich kid who was afraid to go to Vietnam. Of the 32,000 desertions which can be directly related to Vietnam service, 20,000 occurred after the soldier had completed a Vietnam tour. About 7,000 were desertions to avoid going to Vietnam and 5,000 took place in Vietnam - only 24 of which were desertion to avoid hazardous duty.

Many deserters were poor and ill-educated and unconcerned with politics, but suffering personal or family troubles. Only a few were vocally anti-war and prominently covered by the media if their Canadian or Swedish exile.

For the next generation of Americans who may ask what their daddies did in the war, Chance and Circumstance will be an indispensable guide. The fathers who served, as Baskir and Strauss note, were shamefully treated when they returned and given far less support than veterans of other wars. Those who went to prison or exile also paid a price in years and disruption of their lives.

Most, however, whether war or anti-war supporters, found ways to dodge Vietnam. Few saw the war as did John Foote, who told the authors: "Wrongly or rightly, Vietnam had to be faced and it seemed to me then that there were only three ways to face it honorably: go to war, go to jail, or go to Canada."