A sizable increase in aid for hard-pressed sub-Saharan nations seems assured next year after recent pledges made by wealthy nations in conjunction with the World Bank and the International Monetary Fund.

After a meeting in Paris last week, the World Bank announced that 17 donor nations, including the United States, as well as the African Development Bank and the European Economic Community had pledged $3 billion in bilateral aid for cofinancing programs arranged by the bank.

Those funds are in addition to $3.4 billion already committed to the African nations by the same governments and authorities over a three-year period beginning in 1988.

The additional funds are to help sub-Saharan countries boost their economic growth rates.

The funding agreement, according to bank regional vice president for Africa Edward V.K. Jaycox, "is a clear statement of support from the international community for the efforts of these countries to lift themselves out of this crisis."

Officials of the World Bank, IMF and other international agencies at the Paris meeting told donors there was a critical need for cash that could be quickly disbursed.

The officials said the additional funds would support the efforts of individual governments to maintain essential programs, to provide for the poorest in their populations and to carry out other economic reforms.

The Paris agreement is closely related to two other packages for the heavily indebted, low-income countries of Africa: $2.9 billion in no-interest loans through the International Development Association (IDA), the World Bank's concessional aid arm, over the same three-year period, and a sharply increased Structural Adjustment Facility of the IMF.

The IMF plan, first announced at the Venice economic summit earlier this year, will triple from $4 billion to about $12 billion the amount the IMF will be distributing in 60 low-income countries, 34 of which are in Africa, over the three-year period.

Although not all contributions to the facility have been assured, it was learned that IMF managing director Michel Camdessus hopes to announce shortly that he has assembled most of the funds to start the program early in 1988.

Camdessus recently visited Japan, which has agreed to make a major contribution to the program.

The United States' donation to the World Bank's $6.4 cofinancing package will be from the Agency for International Development (AID) appropriations, which have been running at about $650 million a year for Africa, according to AID.

The United States also contributes to IDA, but declined to participate in the IMF facility program, arguing that countries with current account surpluses should be expected to put up money for that program.

According to the IMF, its $12 billion will be made available for countries that adopt strong, growth-oriented economic policies, and undertake to work in cooperation with the bank as well as the IMF.