Despite President Reagan's State of the Union pledge to strengthen the world economy, it now appears likely that the United States will be two years late in fulfilling its current $3.24 billion commitment to the World Bank's so-called soft-loan agency, the International Development Association.

The money originally was supposed to be paid by fiscal 1983; the likelier date is now fiscal 1985.

IDA makes 50-year, no-interest loans, with a 0.75-percent service charge, to poor, developing nations. For the poorest, the agency is the only source of aid money.

Because of its own straitened circumstances, the IDA already is considering charging 3 to 4 percent interest and shortening its loans to 30 to 40 years, bank sources indicated yesterday. A delay in the U.S. contribution would squeeze the IDA even more.

The harder IDA terms would come not only at a time of critical need in the world's worst-off countries in sub-Saharan Africa, but also as IDA raises from 1.2 billion to 2.2 billion the part of the world population it serves. It will do this when it starts accepting loan applications from what could become its largest claimant, the People's Republic of China.

The new U.S. budget to go to Congress Monday, it was learned, will ask for a $245 million supplemental appropriation for IDA for fiscal 1983, to finish the administration's request for $945 million, of which $700 million has already been appropriated.

If the supplemental is approved, that would still leave more than $1 billion to be appropriated to fulfill the $3.24 billion commitment for the current round of IDA lending, called "IDA-6." But administration officials do not expect Congress to approve the supplemental, and also think it highly unlikely Congress will then approve in fiscal 1984 all of the remaining total of $1.34 billion.

"I think what you're seeing is that IDA-6 won't be finished until fiscal 1985," one official said.

The next scheduled "soft loan" aid package for poor countries, IDA-7, is supposed to begin on July 1, 1984. But continued U.S. delay in its contributions has created great uncertainty about IDA's prospects.

Faced with tight budgets in many contributing countries besides the United States, plus the inclusion of China among the recipients, officials said yesterday that the money advanced through IDA-7, whenever it starts, will have to be offered on stricter terms than ever before.

So far administration officials have not said how much money they may commit for IDA-7. There will be no clue in Monday's budget message. But a Treasury report last year indicated that the administration is thinking in terms of a $750 million annual level, or more than a 25-percent reduction from the original $1.1 billion IDA-6 levels.

Since other nations now peg their contributions to the U.S. donation, that would mean an equivalent reduction in the total IDA money pool.

IDA officials will meet in Paris next week to discuss IDA-7.

World Bank officials have virtually abandoned their original goal of pulling together $17 billion in grant money for the three years of IDA-7, compared with $12 billion pledged for IDA-6.

To achieve a $17 billion level, which in real terms--allowing for inflation and the need to help China--would represent a 25-percent reduction in per capita commitments, IDA will have to borrow money from governments or in commercial markets.

The size of the borrowed component would help determine what interest rate would have to be charged for the lendable "mix."

Although final decisions depend on a series of meetings that may continue beyond the September annual session here, officials plan to give first priority on IDA money to the poorest countries, such as Bangladesh and the sub-Sahara area.