The World Bank, the chief source of technical assistance to the world's developing countries, expects to double its capital, and therefore its lending ability, from $40 billion to $80 billion in the 1980s.

Eugene Rotberg, the bank's treasurer, said that a consensus has been reached among the world financial leaders to pump enough resources into the bank to enable it to boost its lending by about 12 percent a year during the next decade.

Rotberg, who met with a group of reporters today, also said the World Bank-which makes long-term loans to developing countries for projects such as dams, power stations and roads-will do no borrowing in world markets during the next three months but expects to borrow about $5 billion in the bank's fiscal 1980, which starts July 1.

Most of the borrowing is likely to be in West German marks and Japanere yen, he said, although the banks may also borrow in dollar-denominated securities.

Because of the steep depreciation of the dollar in recent years, the World Bank has not borrowed in U.S. credit markets in nearly two years.

At the annual meeting of the World Bank and the International Monetary Fund last September, the free world's financial leaders reached a tentative agreement to add between $30 billion and $40 billion to the bank's resources.

World Bank President Robert S. McNamara had pushed hard for such an increase to keep the bank's lending rising about 5 percent per year in real terms (after inflation).

The United States, the biggest investor in the bank, would be responsible for something under $9 billion of that increase. Despite the Carter administration's apparent agreement with the boost in the bank's resources, it remains to be seen whether the administration will be able to convince Congress to go along with the increase.

Congress has been increasingly reluctant in recent years to boost both bilateral aid and multilateral aid. The World Bank and the IMF also have come under strong congressional criticism in recent years because of the high, untaxed salaries earned by their employes.

The World Bank is composed of 135 nations, with most of the resources provided by relatively affluent nations (such as the U.S., Germany, Japan, Britain and France), and most of the loans going to middle-range developing countries such as South Korea or Brazil.

The World Bank has an affiliate the International Development Association, that provides interest-free, 40-year loans for projects to countries that are too poor to qualify for World Bank assistance.

Rotberg said the World Bank paid back 5.6 percent a year for its debt and equity and earns about 7.8 percent on its outstanding loans. Last year the bank made a profit of about $238 million, and Rotberg said it will earn between $350 million and $400 million this year.

The increase in capital that the bank contemplates, which will be presented to the bank's executive board within a month or so, would not require an actual outlay of $40 billion by the world's developed countries.

Something around 6 percent of the increased capitalization actually would be transferred from the nation's to the bank's coffers, while the rest would remain "on call" to cover bank losses in the case of sizable loan defaults.

Rotberg said today that of the $27 billion the bank has on loan to date, only $10,000 is more than 60 days late. He said that by 1982 the bank will reach the $40 billion lending limit it has now.