Latin America is slowly coming out of the deep economic slump of the early 1980s, but income in some countries -- notably Mexico -- dropped sharply last year, the Inter-American Development Bank said yesterday.

"Only three countries -- Brazil, Colombia, Panama -- had a higher {average income} in 1986 than in 1980, while 13 had a loss of at least 10 percent," the bank said in its annual report.

During 1986, average income for people in the region rose by 1.4 percent to $2,140 a year, about the same rate of increase as the previous two years. The lowest annual income of $342 -- less than a dollar a day -- was in Haiti. The highest was $7,884 in the Bahamas.

In March, Latin American members rejected a chance to more than double the bank's lending power, from the present projection of $10 billion to $22.5 billion. The additional money would have been accompanied by a new arrangement that would have given the United States and Canada what amounted to a joint veto over new loans.

"Up to now there has been a surprising degree of public tolerance in the face of unemployment, reduction of social services and the drop in real incomes of the population," the bank said. "Deep social conflicts have been arising in some countries... . The restoration of economic growth could reduce the violence inherent in such conflicts."

The report showed that in Mexico, where the government of President Miguel de La Madrid has accumulated a record $14.6 billion in reserves, average income dropped last year by 6.4 percent, consumption by 4.6 percent and investment by 11.7 percent. The average Mexican earned $2,407 last year, down from $2,734 in 1980.

Activity in the Mexican building industry dropped 12 percent last year. Consumer prices rose 106 percent and foreign debt was close to $100 billion. At the end of 1986, a U.S. dollar was worth 900 Mexican pesos. The price now is over 1,500 pesos.

Other countries did better than Mexico, which has been hit hard by the drop in world oil prices. In Argentina, average income was up more than 4 percent after a drop of 6 percent in 1985. Investment in Argentina rose by 18.5 percent after six years of decline.

Brazil, which accounts for a large part of South America's economy, increased its production by the unusually high rate of 8.2 percent for the third year in a row. But Brazil was troubled by a resurgence of inflation.

And it has a serious problem in its relations with foreign banks since shaking the international financial world in February by suspending all interest payments to them. The Third World's biggest debtor, Brazil owes foreigners more than $111 billion.

Peru increased its production even more than Brazil -- by 8.5 percent -- in part by cutting payments on its foreign debt, another shock to banks. Inflation in Lima, the capital, was still 77.9 percent, but that was less than half what it was the year before.

Colombia had a good year, increasing its total production by an estimated 5 percent -- the first rise in seven years.