The poor regions of the United States became poorer in the 1980s while the rich regions got richer, a reversal of a 50-year trend of narrowing income differences, the Commerce Department reported yesterday.

The decline in the manufacturing, farm and energy sectors of the economy was generally blamed for lower-than-average increases in personal income in the Great Lakes, Southwestern, Rocky Mountain and Far Western regions from 1979 to 1986.

In New England and the Mideast, on the other hand, such fast-growing service industries as banking and health, along with an upturn in defense and high technology, led to a sharp rise in personal income.

New England ranked as the highest-income part of the nation last year, rising from fourth place seven years ago. The Southeast remained the poorest of the eight regions studied by the Commerce Department's Bureau of Economic Analysis.

The District of Columbia had the second-highest income levels of any jurisdiction in the nation after Connecticut, with per capita personal income at 132 percent of the national average, the report said. In 1986, average per capita income for District residents was $19,397, compared with the national average of $14,641. Incomes in the District rose at an 8 percent annual rate from 1979 to 1986.

"It is mainly the fact that the District does not have the typical industrial base," said Rudolph E. DePass, a regional economist with the BEA. "Manufacturing and durables are almost nil. It is a tourist area, and that brings in a lot of income. Government is very heavily represented {along with} business services. Many are indirectly related to government, and there are a lot of lawyers."

Maryland ranked seventh among the states in 1986, with personal income of $16,864 and an average rate of increase over the last seven years of 8.3 percent. Virginia was the 11th-ranked state, even though its per capita income of $15,408 was only 5 percent above the national average. Per capita income rose 8.5 percent per year from 1979 to 1986 in Virginia.

Regionally, the Commerce figures showed that income differences between parts of the country narrowed steadily from 1929 to 1979. In 1929, per capita income in the richest region, the Mideast, was 138 percent of the national average. Income in the poorest, the Southeast, was 53 percent of the national average.

In 1979, the richest region, the Far West, was only 114 percent above the national average while the poorest, the Southeast, was 85 percent of the average. By 1986, the richest region, New England, had per capita income at 117 percent of the national average, although the Southeast, still the poorest, had improved its standing slightly to 87 percent. All three regions with incomes above the national average were more than 10 percent above it last year, while only one region was more than 10 percent richer than the average in 1979.

"You could say this pattern reflected the falloff in industry, agriculture and the mineral heartland of the country, while service businesses and financial services prospered in the Mideast and defense-related and other services prospered in New England," DePass said.

In the Southeastern region in particular, he said, income growth was much stronger in coastal states, including Virginia, than it was farther inland. Maryland showed growth in service industries and, DePass said, an influx of companies coming into the state to take advantage of relatively low costs of doing busines