Reform efforts of the United Nations Educational, Scientific and Cultural Organization amount to "small change," making chances "very, very slim" that the United States will remain in UNESCO, Gregory Newell, assistant secretary of state for international organizations, said yesterday.

President Reagan announced last year that the United States would withdraw this month if reform was not forthcoming, and a formal withdrawal announcement is expected within days.

Newell made public a 15-page report of the State Department's official civilian monitoring panel on UNESCO, which found that, "while there was considerable discussion and some incremental movement" in UNESCO this year toward reform along the lines demanded by the United States, "there was no concrete change."

This report differs sharply from another, made public Wednesday, by observers from the U.S. National Commission for UNESCO, a citizens' group established by Congress in 1946 to act as liaison between the international organization and nongovernmental groups, scientists, educators, artists and other individuals.

Two commission members wrote in that report that a seven-month U.S. delay in spelling out reforms it wanted "greatly hampered" UNESCO's reform efforts, and they asserted that most U.S. allies want the United States to remain in the organization.

The State Department document, however, said most developed nations back the U.S. view that serious reform is needed in three areas: to reduce the number and scope of UNESCO programs and depoliticize them; to protect the interests of UNESCO's major funders, the western nations who are routinely outvoted by Third World nations, and to decentralize operations so as to involve more private sector and intergovernmental bodies.

"Most developing countries resisted fundamental, structural proposals," the monitoring group report said.

"The Soviet Union actively sought to undermine the reform process . . . . The UNESCO Secretariat, which openly sides with developing states on most issues, continued to do so in 1984," the report said.

Newell spoke at the annual meeting of the commission, which voted to ask to stay in existence as an advisory group even if the United States withdraws from UNESCO.

He commended the commission on its work but was not reassuring about its future.

Newell said that "an unacceptable gap clearly remains" between U.S. demands and UNESCO performance.