MEXICO CITY (AP) _ The September earthquakes that devastated sections of the Mexican capital killed 6,000 people, injured 30,000 and caused property damage estimated at $4 billion, a report by a United Nations commission says.

Another 2,000 people are missing and presumed dead, buried under rubble, according to the report by the Economic Commission for Latin America. The report was prepared by U.N. experts ''in close consultation with Mexican authorities'' and released here this week.

Mexican newspapers described it is the most authoritative survey so far of damages caused by an earthquake that measured 8.1 on the open-ended Richter scale Sept. 19, and one measuring 7.5 a day later. Seventy-seven aftershocks were felt in the week that followed.

The report said the earthquakes seriously affected an area of 320,000 square miles, were felt by almost 20 million people, and about 150,000 people suffered property damage. An estimated 30,000 people were rendered homeless and forced to live in temporary shelters.

''The earthquake caused considerable damage to housing, health and education, with high financial costs, aside from damages impossible to assess to murals, historical and archeological monuments, whose value is impossible to estimate,'' the report said.

A total of 3,300 ''major buildings'' were destroyed or damaged in Mexico City, including apartment and office buildings up to 15 stories high, hotels, hospitals, theaters, schools and 125 buildings housing government agencies, according to the report.

About 30,000 housing units were destroyed and another 60,000 were damaged, aggravating an existing housing shortage that before the earthquake were estimated by government sources at three million units, the report said.

A unit was defined as an occupied room or group of rooms that is not shared with other tenants of a building. Thus, a single-family house would count as one unit, and an apartment building with 10 separate aprtments would count as 10 units.

According to the report, health-care services were the most seriously affected. Five hundred hospital and clinic buildings were damaged and nine were destroyed, causing a total loss of 5,000 hospital beds.

The quakes destroyed 137 school buildings and damaged 313, leaving 150,000 students without a place to study. Five hotel buildings collapsed, four more were severely damaged and another 36 need extensive repairs, it said.

Seven of the capital's 250 movie theaters collapsed and 49 had to be closed for extensive repairs, the report said. But most bars and nightclubs were not seriously affected.

According to the report, the earthquake lasted one minute at the epicenter, just off the Balsas River in the Pacific Ocean, but was felt for up to three minutes in metropolitan Mexico City, an area where 18 million of the country's 78 million people live.

It was also felt strongly in the central states of Jalisco, Guerrero and Michoacan, the report said. But it described the situation in the capital as ''critical'' and said most of the devastation occurred in about 14 square miles in the city's center.