The World Bank reported yesterday that it has cut the lending rates and fees it charges Third World loan customers because of its extraordinary profit of $588 million in the first half of fiscal 1985, which was almost as much as the $600 million it earned in all of 1984.

The bank's lending rate was reduced effective Jan. 1 from 9.89 percent to 9.29 percent.

Moreover, Senior Vice President for Finance Moeen A. Qureshi said yesterday that the front-end fee of 0.25 percent introduced three years ago would be reduced to zero but kept available for future use.

Details of its investment strategy showed that the bank has been keeping its assets in high-yielding dollar obligations and its liabilities in other currencies that have been depreciating. The result has been lush profits that the bank is now being pressed to use for the benefit of its poorest members.

Meanwhile, Treasurer Eugene Rotberg revealed that since most of the World Bank's regular loans are denominated in Japanese yen, Swiss francs and West German marks -- all of which have depreciated sharply against the dollar -- the borrowing nations could save as much as $6 billion, "if all of the $31 billion in loans disbursed by the bank over the past seven years were to be repaid now."

Rotberg explained that, with most other currency rates severely depressed against the dollar, debtor countries could buy the equivalent of the $31 billion in Swiss francs, marks or yen for about $25 billion in dollars. He said that before the dollar shifts the other way, some of these countries would be wise to pay off large amounts of their debt.

Qureshi also said that the bank's soaring profits are due in large part to the money-management operations supervised by Rotberg.

Part of the bank's investment profits -- expected to hit $900 million for the full fiscal year 1985 -- will be allocated to World Bank reserves, Qureshi said. But part of it, said Rotberg, "can be used as a dividend where it will do some good." Last year, $200 million of the bank's $600 million profit was passed on to the International Development Association, the bank's concessional aid arm. This year's share for IDA, presumably larger, is to be decided later on.

Qureshi said the bank is now "in a very strong position, not only from the profit perspective, but from the standpoint of being able to fund itself, regardless of the circumstances, from the capital markets."

At the same time, he confirmed reports that World Bank loan commitments this fiscal year are expected to fall by about $2 billion from an earlier projection of $12 billion to $13 billion, and that a proposal for a new capital increase would not be made until the bank's annual meeting in October.

The return on short-term dollar investments in the first half of fiscal 1985 was 14.16 percent, against 11.19 for short-term non-dollar investments. On a book-value basis (interest rates plus realized gains) the average yield was 13.55 percent, compared with 9.81 percent for the first half of fiscal 1984.

But the financial rate of return on short-term dollar investments -- which includes unrealized gains as well as realized gains -- comes to an even more spectacular 17.62 percent, Rotberg said.

Part of the bank's excellent financial scorecard can be traced to a program of currency swaps that enabled the bank to benefit from soaring dollar exchange rates.

Qureshi said that "the judicious timing of issues and choice of currencies" had enabled the bank in the last six months of 1984 to borrow $6.3 billion in 10 national currencies at an average cost of 7.82 percent, compared with 8.09 percent in the same period of 1983.

There were some "random" events that contributed to the profit record, Rotberg said. "But there [were] also some obvious things where you couldn't help but make the right decision. You would have to have been foolish not to take advantage of the opportunities. There were some wise perceptions by some very smart people."

Rotberg said the bank intends to borrow $12 billion worth of currencies this year at an average cost of 8.3 percent, slightly higher than the first-half 7.82 percent average.