The nation's economy grew at a sluggish annual rate of 1.3 percent in the first quarter, the government said yesterday in a revision of initial figures.

The growth was slower than first thought because of what analysts consider a healthy reduction in business inventories.

But while the Commerce Department report lowered the January-March growth rate, it pumped up the inflation rate from 6.5 percent to 6.7 percent -- the highest level since it reached 7.7 percent in the fourth quarter of 1981.

While the inventory reduction was considered a possible sign of future growth, the first-quarter gross national product was weaker than the original 2.1 percent estimate last month and only slightly improved from the fourth quarter's 1.1 percent rate.

The growth rates in both quarters were the weakest since the economy grew at a 0.8 percent rate in the July-September period of 1986. The GNP measures the nation's total output of goods and services.

The Bush administration initially forecast 2.4 percent growth this year, and the new report spells more problems for administration and congressional budget negotiators as they resumed talks yesterday on cutting the deficit.

''If the slow, near 1 percent growth of the last two quarters persists, government revenues will be down $15 billion from projections in 1990 and will be down $45 billion in 1991, greatly adding to the budget and deficit problems,'' said Richard W. Rahn, chief economist of the U.S. Chamber of Commerce.

The first-quarter GNP revision came after additional information was gathered showing an $8.5 billion downward revision in business inventories. The department will publish its final reading on the first-quarter economy next month.

The price index tied to the GNP jumped from 3.6 percent in the fourth quarter to 6.7 percent from January through March. ''About half of the step-up was due to food and energy prices,'' the department said.