As President Reagan and Soviet leader Mikhail Gorbachev prepare to meet in Geneva in an attempt to slow the arms race, private groups and the Defense Department itself have, for different reasons, come up with some eye-popping statistics on military efforts around the world.

The world is spending$800 billion a year on military programs and has enough nuclear weapons to kill 58 billion people, or every living person 12 times over, according to a recently issued report, "World Military and Social Expenditures 1985" by Ruth Sivard, a former official of the U.S. Arms Control and Disarmament Agency and now director of World Priorities, a nonprofit research organization.

There is one soldier for every 43 persons in the world, compared to one doctor for every 1,030 persons, the report continued, and the average car would cost $300,000 if its price had gone up as much as that of sophisticated weapons since World War II.

There have been four times as many war deaths in the 40 years since World War II than in the 40 years preceding it, Sivard calculated. The Soviet Union lost the most to war in the 20th century: 22.4 million people. Within that total, World War II claimed the lives of 7.5 million Soviet civilians and 7.5 million Soviet military personnel. The United States suffered 408,000 military deaths and no civilian deaths in World War II combat, the report said.

The killing power of sophisticated weapons has increased two hundredfold since World War II, the report said, citing as one example the increase in firing power of machine guns over the last 40 years: from 250 to 6,000 bullets per minute.

"The Soviet Union," said Sivard, "in one year spends more on military defense than the governments of all the developing countries spend for education and health care for 3.6 billion people."

Funding for Sivard's report came from the Arms Control Association, World Policy Insitute, Peace Through Law Education Fund, Rockefeller Foundation, Stanley Foundation, Committee for a Sane Nuclear Policy, United Nations Association of Australia, Canada's Project Ploughshares, British Council of Churches and United Nations Association of Sweden.

Sivard wrote that "the purpose of the report is to provide an annual accounting of the use of world resources for social and for military purposes, and an objective basis for assessing relative military priorities."

The Pentagon issues several statistical reports on the U.S. military effort, including how the money is distributed among the states. The latest report shows that California remains the largest beneficiary of defense spending, netting $28.5 billion in defense contracts in fiscal 1984, the latest date of record, compared to $17.3 billion in fiscal 1981.

California ranked first even before Reagan's rearmament program took hold, and stayed in that position in the subsequent three years. Ranking behind California in the top 10 in fiscal 1984 defense contracts were: New York,$9.5 billion; Texas, $8.7 billion; Massachusetts, $7 billion; Missouri, $6.5 billion; Connecticut, $5.5 billion; Virginia, $4.6 billion; Florida,$4.03 billion; Maryland, $4.01 billion, and New Jersey, $3.3 billion.

The District of Columbia, thanks largely to contracts the Pentagon awarded to the Energy Department for nuclear reactors, netted$815.5 million in defense contracts in fiscal 1984, only slightly less than the whole state of North Carolina.

Military installations in the 50 states and District of Columbia take up 24 million acres, according to the Pentagon, with 1,658 acres in the District; 127,931 in Maryland and 268,228 in Virginia.

REFORM DRIVE . . . Defense Secretary Caspar W. Weinberger is scheduled to testify before would-be Pentagon reformers on the Senate Armed Services Committee today on how to get more bang for the buck. Pentagon insiders predict that Weinberger will be less unbending on reform proposals than he has been on proposed budget cuts.