Smaller industrial and developing countries appear to be skeptical of a Reagan administration proposal to hold a conference of major developed countries to try to improve the international monetary system.

Several top financial officials of these countries -- gathered here for a meeting of the International Monetary Fund's Interim Committee -- said privately that they object to the prospect of the bigger nations sitting down without them. They said they want debate about reform of the system to include a large number of countries. Smaller nations maintain they have as much at stake in the fluctuations of exchange rates as the giant industrial countries.

The smaller nations see the conference proposed last week by U.S. Treasury Secretary James Baker as a way to keep any changes in the system of freely floating exchange rates under control of the United States and other major countries -- including, presumably, Japan, West Germany, Britain and France.

Argentine Economy Minister Juan V. Sourrouille , who heads the so-called Group of 24 developing countries, said developing countries want a complete reform of the international monetary system to eliminate the wide swings in exchange rates that have such a devastating impact on smaller nations. He said developing nations should be part of an international conference to overhaul the system.

Baker's proposal for a conference marked an abrupt shift in an administration position that no such meeting was needed. The assistant U.S. Treasury secretary for international affairs, David Mulford, emphasized yesterday that the proposed conference would not consider a complete overhaul of the international financial system -- as France has suggested -- but would deal merely with specific "improvements" that might be made.

In a press briefing, Mulford mentioned proposals to ensure that the world's nations coordinate their economic policies more carefully and that the International Monetary Fund enhance its surveillance of the economic policies of all its member countries, not just debtor nations.

Mulford said the proposed conference would not be an alternative to the IMF -- which oversees the international financial system -- but would enhance the IMF's role by presenting specific proposals for its so-called Interim Committee to debate. Mulford said the United States is willing to host the session, but he ruled out participation by developing nations.

The developing countries are represented in the Interim Committee, which would have to make any decisions on overhaul. But several financial officials said that by controlling the input to the Interim Committee -- set up more than a decade ago to study changes in the world financial order -- the United States and other big nations will ensure that more broadly based reform proposals do not get off the ground.

Mulford said the conference would rely upon a soon-to-be-completed study of the system undertaken by the Group of 10 industrial countries. That study is expected to conclude that no overhaul of the system is needed.

The Group of 24 developing countries called in a communique for dozens of changes in the international economic order, including establishment of an IMF fund that would subsidize interest payments of debtor nations, an increase in the lending authority of the development-oriented World Bank and establishment of a task force within the World Bank-IMF Development Committee to study mechanisms for alleviating the burdens of international debt.

Mulford said the United States remains cool to most of these proposals.