Leading members of a national advisory commission have challenged President Reagan's decision to withdraw from one of the largest United Nations organizations.
The executive committee members of the 100-member US National Commission for UNESCO charge that the United States will diminish its influence in a number of fields if it leaves the United Nations Educational, Scientific, and Cultural Organization.
The commissioners say the withdrawal decision ran counter to the recommendations of 13 federal agencies and was not supported by 83 US embassies and consulates around the world.
A 30-page document released by the national commission's executive committee amounts to the first substantive challenge to President Reagan's decision, announced in December, to withdraw from UNESCO. At hearings earlier this year, some members of a US House subcommittee questioned the withdrawal decision.
At press conferences held yesterday in Washington and New York, advisory commission members said that they share some of the Reagan administration's criticisms, but that they also found value in many of UNESCO's programs. They argued that reforms sought by the US and its allies would be best achieved by working within UNESCO and not by walking out of it.
In New York, Leonard R. Sussman, a vice-chairman of the advisory commission, charged that Gregory J. Newell, the assistant secretary of state who conducted an administration review of UNESCO activities, had distorted facts relating to the withdrawal decision and substituted ''ideological dogma'' for honest debate.
The Reagan administration notified UNESCO at the end of last year that it would withdraw from the organization, effective Dec. 31 of this year. It charged that UNESCO had ''politicized'' virtually every subject it handled, exhibited hostility toward the basic institutions of a free society, and engaged in unrestrained budgetary expansion. But the administration also left open the possibility of reversing its decision, should UNESCO take into account the views of the US and other Western nations and ''restore fiscal integrity'' to the organization.
This year the US is contributing $25.8 million to UNESCO, according to the advisory commission.
The US National Commission for UNESCO, established by Congress in 1946, is charged with providing information on UNESCO and consulting with the US State Department concerning the organization. Of the 100 commissioners, 60 are from nongovernmental organizations such as the National Academy of Sciences; 25 represent state and local governments; and 15 are appointed by the administration.
Last December, commission members voted 41 to 8 in favor of the US staying in UNESCO. A later vote was 57 to 17 in favor of retaining membership.
The 30-page report released yesterday was approved by 16 of the 18 members of the commission's executive committee. One member abstained for ''personal reasons,'' and one could not be reached, an executive committee member said.
The report says US evaluations of the 1983 biennial UNESCO general conference were mostly positive and that UNESCO ''has been no more politicized than other international organizations.''
The UNESCO budget had only a small increase this year, and only about 1 percent of the organization's budget is spent on programs which the State Department believes are ''highly politicized,'' the report says, adding that few of the substantive educational, scientific, and cultural programs are politicized.
The report says the Soviet Union does not exercise a major influence on UNESCO programs, although it has taken a more active interest in the organization than have recent US administrations. Only 8 percent of UNESCO staff members come from Eastern-bloc nations, it says. The US has the largest number of staff members of any nation - 82 of 814 at the end of 1983.
The report argues that when the US has exerted strong leadership, it has achieved its goals at UNESCO. It further states that UNESCO has taken no actions to limit press freedom, and that proposals threatening the free flow of information have been repeatedly rejected in the organization's deliberations.
In New York, commission member Sussman told reporters the administration had decided to withdraw from UNESCO even before Assistant Secretary of State Newell began his review of international organizations in mid-1982. The campaign to withdraw actually began, Mr. Sussman said, when David A. Stockman, director of the Office of Management and Budget, struck UNESCO from a draft budget even before taking office in 1981.
In answer to a question during congressional testimony last May, Newell said that before the decision to withdraw from UNESCO was made, he had consulted ''widely'' with Freedom House, a nonprofit, New York-based organization. Sussman , the executive director of Freedom House, said Newell's assertion was incorrect and that he had received ''no more than the official line'' after the decision to withdraw had already been made.
Sussman described Newell as ''the manager of an ideological position that would support withdrawal from UNESCO at all costs.''
Sussman, who was invited to Paris recently to give advice to the UNESCO director general on communications matters, said there is ''decided movement'' within the organization towards reform. ''The only country that wants us out of UNESCO is the Soviet Union.''