The Soviet economy has made one of its worst starts in postwar years, according to official figures released today, despite a relatively mild winter in most of the country's industrial heartland.

The weekly Economic Gazette reported that industrial production in January and February increased just 2.6 present compared with the first two months of 1980, well short of the annual goal of 4.1 percent industrial expansion called for in the 1981 plan.

Labor productivity, a crucial factor accounting for 90 percent of all economic industrial expansion through 1985 under the new five-year plan, rose only 1.8 percent in the two months, just half the increase charted in the current economic outline.

Oil production rose 0.8 percent, which is lower than called for, while steel production decreased by 0.1 percent from the same period last year, and coal production fell by a half a percent. Natural gas, which is scheduled to rise by 50 percent through 1985 and became a greater export item than ever before as the country slows the growth of its petroleum exports, rose by 7 percent in the first two months of the year. This is on target, according to the plan.

At last month's Communist Party Congress, President Leonid Brezhnev warned that much larger increases in worker productivity were essential if the economy was to expand. The official Economic Gazette did not give reasons for the below-norm results in oil, coal, and steel. Reported actual declines in production totals likely mean major difficulties in those industries, since the figures are based on gross output and do not take into account substandard production rejected as unusable.

Meanwhile, Soviet meat production declined from the first two months of 1980, when distress slaughters pushed production up in the face of feed shortages aggravated by the U.S. grain embargo. Meat production was down 6.2 percent for 1981 so far, but the average slaughter weight of cattle was 802.6 pounds, a 2.2-pound increase from weights reported a year ago. This indicates the Soviets have had some success in solving their persistent feed problems.

Slaughter weights for pork also showed a 6.6-pound increase from the same period a year ago, and poultry production was up 9 percent from last year.U.S. Department of Agriculture forecasts predict Soviet meat production will drop to 14.8 million tons from 15.1 million reported last year, which means that, with the population rising, actual per capita meat production will be noticeably down.

These decreases come as the Soviet leadership faces likely requests from Poland and Afghanistan for additional food aid.

It is thought possible Moscow may eventually have to pay hard currency for major foreign meat purchases if the production problems continue.