The Soviet Union's troubles with food and petroleum production were confirmed by final official economic figures today, which indicated more problems in these crucial sectors in the future.

Government statisticians said the 1980 grain harvest totaled 189.2 million tons, a slight improvement over earlier official estimates for the year, but more than 45 million tons below the year's goal. The second harvest disaster in a row and the third in the last five years contributed to an overall decline of 3 percent in total farm output last year from 1979, with meat, milk and wool production registering declines.

The effects of these shortfalls have been magnified by the continuing steady growth of the Soviet population, which the official Tass news agency today said topped 266 million at the end of the year.

Declines in meat production of about 3 percent reflect smaller carcass weights because of poor fodder, a situation aggravated by the U.S. grain embargo of cattle and other livestock feed. Foreign analysts doubt that Moscow will be able to reach its goal of 240 million tons of grain annually, called for in the new five-year plan to be adopted at next month's Communist Party congress.

Officials confirmed at a press conference that petroleum production reached 603 million tons (12.96 million barrels per day) last year, 3 million tongs below target. While the shortfall is statistically insignificant, it bodes ill for the years ahead. The CIA has predicted that the largest oil producer, now with oil exports to Western Europe as well as its Eastern satellites, will become a net importer by the mid-198os.

The Soviets achieved a 17 million ton increase last year in oil production above 1979 totals, but have projected only a 7 million ton increase for 1981, a flattening out of expectations that could indicate the CIA's predictions ultimately may prove right. However, Moscow has undertaken crash energy conservation programs and a major exploration effort in the western Siberia, and set a 50 percent rise in natural gas output by 1985.

Figures showed the Soveits achieved the goal of producing 435 billion cubic meters of gas for 1980, an increase of almost 5 percent over 1979. But coal output declined by 3 million tons from 719 million tons in 1979.