The resolution of the Third World debt problem "is likely to take longer than was expected," but the basic debt strategy devised two years ago by Treasury Secretary James A. Baker III should not be altered, the political officials who manage the International Monetary Fund said yesterday.

The IMF's Interim Committee, which met here over the weekend prior to the opening this morning of the annual IMF/World Bank meeting, admitted that the debt crisis was not responding to help as quickly as had been hoped, in part because of low commodity prices and a recent trend of higher interest rates.

But in a long communique, the Interim Committee -- to the dismay of Third World participants -- urged staying pretty much with the Baker "case-by-case" approach to debt strategy, except for modest refinements in the form of "market-oriented options" that the banks might substitute for traditional loans.

"This is the only way in which adjustment programs and financing flows can be tailored to individual country circumstances," the communique said.

Baker's plan, unveiled two years ago at the annual IMF/World Bank meeting in Seoul, called on the multilateral and commercial banks to expand their loans to 15 major debtor countries on condition that those countries undertake specific economic reforms to boost efficiency and growth.

But the debtor countries have openly and bitterly challenged the Baker Plan, warning that they see it as a stand-pat policy that can lead to defaults.

A report over the weekend by the Group of 24, a steering committee for the poor nations within the IMF, said that the 1980s are becoming "a lost decade" for the developing nations.

The Interim Committee, in an apparent rebuke to the G-24 for that warning, said that "unilateral initiatives carry heavy risks for all parties."

Instead, the committee urged the large debtor countries to put more effort into domestic reforms, stressing "the overriding need for heavily indebted countries to pursue policies aimed at restoring macroeconomic balance and domestic confidence and enhancing growth prospects so as to strengthen creditworthiness, induce a reflow of private capital and ease a return to normal debtor-creditor relations."

The committee conceded that some middle-sized debtor countries have taken such steps and improved their creditworthiness, only to be rebuffed by the banks when they sought easier credit terms.

IMF Managing Director Michel Camdessus said the IMF will "suggest special care" be taken by the banks to make sure that the progress made in these smaller countries is not jeopardized by slowness of the banks to act.

Other IMF sources said that Costa Rica is a case in point. That country has made what is considered to be a good adjustment to its economic problems. But large banks, frustrated by Brazil's moratorium on paying interest on about $70 billion worth of debt, have in effect barred any help to Costa Rica until their problem with Brazil is settled.

Camdessus, asked about the Interim Committee's forecast that the debt problem would take longer to solve than had been anticipated, said that "even if we have to stay longer with the strategy, everybody {expects} that the solution can finally be obtained.

"This is to make the point that even if we take longer, the strategy remains accurate," he said.

The subject of interest rates was also brought up by French Finance Minister Edouard Balladur and German central bank president Karl Otto Poehl.

"Interest rates are too high because currency rates are not stable enough," Balladur said at a breakfast press conference.

He called on the United States, West Germany and Japan to reduce the large trade and current account imbalances among them.

He noted that the Louvre accord of last February, pledging policy action to stabilize exchange rates "around current levels" -- the same pledge reiterated Saturday by the Group of Seven major industrial nations and endorsed yesterday by the Interim Committee -- contains no reference to interest rates.

"We don't make public the level of our intervention, we don't say what our central banks are going to do, and we don't say at what levels we're going to intervene.

"The same is true of interest rates -- a certain amount of uncertainty is useful," Balladur said.

Poehl, the chief German representative here in the absence of Finance Minister Gerhard Stoltenberg, who returned home Sunday night because of a political problem in Schleswig-Holstein, confirmed that officials of the G-7 had talked about interest rates over the weekend. He didn't reveal the gist of the discussion, but said that his central bank had not changed interest rate policy.

Poehl also said that he feels a recent small rise in German money market rates is "worrisome," but didn't indicate what, if anything, the Bundesbank intend to do about it.

On other issues, the Interim Committee:

Welcomed "the progress" toward exchange rate stability made since the Louvre accord, and said that the executive board would continue to work on refining the economic indicators used to help monitor economic performance.

Denied that there is an "impasse" blocking Camdessus' effort to triple the $3 billion in soft-loan money the IMF can make available to Africa. Camdessus acknowledged that donor countries have not yet agreed how to share the burden of the extra $6 billion, but predicted an end-of-year deadline would be met.

Took no action -- except to arrange for further study -- on a ninth general review of quotas, or new resources, for the IMF. But, as suggested by the United States, the enlarged borrowing rights for member countries were extended for another temporary period.

Again ruled out a new issue of special drawing rights (SDRs), the IMF's convertible paper currency, although many countries continue to see the need for this supplement to reserve assets.

James Rupert of the Washington Post Foreign Service also contributed to this report.