The Reagan administration, under pressure from Congress and Southeast Asian nations, is making plans to begin its first direct and open aid to the noncommunist Cambodian resistance, according to State Department sources.

The aid is a relatively small program of educational assistance to enable the noncommunist rebels to administer and govern Cambodia if their cause is successful. An official said it would involve U.S.-furnished training for government administrators and educational, medical and other nonmilitary personnel, "what we used to call nation building" in Indochina one or two decades ago.

The significance of supplying teachers -- but not guns -- would be mostly symbolic and political, officials said. Until now, open U.S. aid to the Cambodian resistance has been solely humanitarian, furnished indirectly though the U.N. Border Relief Agency, which operates along the Thai-Cambodian border.

Former Cambodian chief of state Norodom Sihanouk and former Cambodian prime minister Son Sann, who head the two noncommunist resistance groups, have been asking for direct assistance, including military assistance, from the United States. U.S. policy has been not to furnish direct and open aid to these groups, though there have been persistent reports that some secret funds have been channeled by the Central Intelligence Agency through Southeast Asian nations.

The United States furnishes no aid of any sort to the other coalition partner in the Cambodian resistance, the communist-led Khmer Rouge forces under Pol Pot. China furnishes weapons and other support to the Khmer Rouge and, to a lesser extent, to the noncommunist factions.

Foreign ministers of the Association of Southeast Asian Nations (ASEAN), the main organization of noncommunist nations in the region, called on foreign powers Feb. 11 to step up aid, including military aid, to the resistance groups.

Last Wednesday the House Foreign Affairs subcommittee on Asian and Pacific affairs authorized $5 million in "appropriate aid" to the noncommunist resistance. Several lawmakers indicated that they have military aid in mind, drawing a parallel with U.S. military help given the Afghan resistance.

The administration did not request this authorization and has been critical of the idea. Assistant Secretary of State Paul D. Wolfowitz told the Senate Foreign Relations subcommittee on East Asian and Pacific affairs Thursday that he is unsure what would be accomplished by the House subcommittee plan, adding, "I'm not sure the House quite knows." Wolfowitz, at the Senate hearing, made the first mention of a possible educational program for the Cambodian resistance.

House subcommittee Chairman Stephen J. Solarz (D-N.Y.) called the $5 million authorization "a small but significant contribution to demonstrate that the United States is willing to put its money where its mouth is" in supporting noncommunist Cambodians and "to send a signal to the Vietnamese" that the international community is concerned about the fate of Cambodia.

Rep. Jim Leach (R-Iowa), opposing the authorization, said, "The United States ought to know well by now the liabilities of military involvement in land wars in Asia and ought not to head down that road again without a compelling case and a consensus between the executive and legislative branches." Leach said U.S. military involvement, especially public involvement, would transform the anti-Vietnamese resistance "into a U.S. military operation."

An unusually strong and successful Vietnamese dry-season offensive since late last year has driven nearly all of the Cambodian resistance forces out of their bases along the Thai-Cambodian border. With their camps abandoned under severe Vietnamese attack, the Cambodians have retreated into Thailand.

Any U.S. direct assistance, including the proposed training program, for logistical reasons could be undertaken only with Thai cooperation, State Department sources said. Informal discussions about an educational program have been started with Thailand, the officials said, and more formal talks are expected to be started soon.

If Thailand and other noncommunist Asian nations approve, a team of U.S. experts is likely to be dispatched to the area soon to examine the feasibility of a nonmilitary U.S. educational program.