As a practitioner of one of the quieter callings -- clarification -- Ruth Leger Sivard is herself a woman of reserve and damped-down emotions. With what she knows, she has every right to get on a rooftop and scream. Instead, after 10 years of analyzing what 142 of the planet's governments spend their citizens' money on, she remains a clarifier. The field is small. Few are as skilled.

Sivard, who is 69 and lives with her husband in Georgetown, has again displayed her large talents by publishing the 10th edition of "World Military and Social Expenditures." It is a 52-page gathering of facts, figures and conclusions. With spectacular inerrancy, Sivard lays out the meaning of 142 governments spending more than $800 billion a year on their militaries.

A reading of the 10th edition is a confirmation of the first edition, published in 1974: Militarism is laying waste to every part of the populated Earth. What were inklings then are certainties now. In 10 years, global military expenditures have increased more than 40 percent, in constant prices. The number of unemployed people in 21 developing countries has doubled in one decade.

In the 20th century's first 85 years, 78 million people -- mostly the poor fighting other poor -- have been killed. That is a 500 percent increase over the 19th century. Since 1900, 207 wars have been fought. Developed countries have spent an average of 5.4 percent of their gross national product on their militaries, compared with .3 percent on development assistance to poorer countries.

This spillover of numbers is a small part of the larger truth that hits home by the time all of Sivard's report is read: The results of conventional war are one immense devastation, the effects of a global war-preparation economy are the other. These twins of violence lead Sivard to conclude: "In contrast to the military world of plenty, the real world of the 1980s is one of increasing disparity within, as well as between, nations and crushing poverty for at least one-quarter of humanity. There are more unemployed, more illiterates, more homeless, more people without health services, more unable to satisfy basic needs for food and clean water . . . There is no global security. Governing authorities who expect to achieve it through military power and the suppression of protest have lost touch with reality and their own sense of humanity."

In a second-floor study in her home, Sivard spends a fair amount of time giving interviews. Reporters have come to rely on her because no other document brings together with such precision the relationship between spending for arms and non-spending on peace. Sivard, whose research is supported by several foundations, has published 25,000 copies of her new report. The last one, in 1983, had two reprintings for a total of more than 30,000 copies. The goal, she says, is to persuade the public to understand not only what war and preparing for it are costing in taxes but to realize also what is lost in the trade-offs: "We are all involved. The money comes out of our pockets, and it may kill us."

Sivard, a 1937 graduate of Smith College, worked with the U.N. Relief and Rehabilitation Administration in Austria and the International Refugee Organization in Switzerland. Her career came together, or so she thought, at the U.S. Arms Control and Disarmament Agency. She was appointed chief of the economics division in 1968. Part of her work was to provide public information on military spending.

She left the agency in 1973. Its budget was cut, with no funds for informational documents. In addition, the Defense Department had been demanding to review her publications before release. Recalling that this was "not a climate I felt I could achieve anything in," Sivard decided to do on her own what the government wanted hushed. She formed World Priorities, the research group that publishes "World Military and Social Expenditures."

The public knows something of the gigantic spending on nuclear armaments. Sivard provides details on conventional war that are similarly striking. Currently there is one soldier per 43 people in the world, against one physician per 1,030 people. Saudi Arabia ranks first in the amount of money that a government anually spends per soldier ($500,865). But Saudi Arabia is 120th in its literacy rate. Finland ranks first in literacy but 34th in expenses per soldier. In the developing countries, militarized power is rising. In 1960, 28 percent of independent Third World countries were military controlled; today, 50 percent are.

In the United States, the problem is military extravagance. If price increases had occurred in civilian goods as they have in weapons systems, an average car would cost more than $300,000. And Sivard's report would be going for $1,000, not the $5 bargain that it is.