Riggs National Corp., saddled with more than $100 million in loans to debt-ridden Mexico and Brazil, will pull back from foreign lending, chairman Joe L. Allbritton told shareholders yesterday.

"We're not going out of the international lending business," Allbritton said. But he said foreign loans will not grow "at as rapid a rate" as they did in recent years. "We will re-emphasize our basic constituents--the District, Northern Virginia and Maryland."

In the coming years, he said, Riggs' domestic loan portfolio should grow faster than its list of foreign loans.

Allbritton said that foreign loans made by Riggs National Bank, the only asset of the parent Riggs National Corp., would be chosen "carefully" and on a "conservative basis."

For years Riggs has been the most important banker to the large embassy and foreign mission population in Washington. Like many other regional banks in the late 1970s and early 1980s, it began to participate heavily in loans to foreign governments, especially in Latin America, where profits were big and risks were perceived to be small.

International loans were the fastest growing portion of Riggs' total loan portfolio in 1980 and 1981. But economic difficulties in Brazil and Mexico--as well as many other developing countries--made many of those foreign loans questionable.

Allbritton, speaking at the company's annual shareholders meeting, said that Riggs has about $65 million at risk in Mexico and another $53 million in loans outstanding to Brazil. The Mexican loans represent about 2.5 percent of the bank's total outstanding loans and the Brazil loans equal about 2 percent of the bank's total loans. Riggs has total assets--including loans, securities and other investments--of about $3.7 billion.

Allbritton said that he expects the bank will recover in full its loans to Brazil, but was more cautious in his assessment of Mexico. He merely said it "is difficult to predict the final outcome" and that Riggs officials "are following developments carefully."

The Texas financier--who bought financial control of Riggs about two years ago and ousted the bank's management last fall because of deteriorating profits and rising problem loans--said the bank believes it has adequate reserves to protect itself against losses in its foreign lending.

Mexico and Brazil are rescheduling tens of billions of dollars of debts with the world's banks. In return for loans from the International Monetary Fund, both nations have agreed to reduce domestic spending and to take other austerity measures designed to reduce their need to borrow.