The United States is preparing to send consular officials to Vietnam for the first time since the communist takeover to process visas for refugees wishing to join family members here, the State department announced yesterday.

Deputy Assistant Secretary of State Robert B. Oakley said the U.S. officials will go to Ho Chi Minh City "In a matter of weeks" if details can be worked out with the Vietnamese government and the United Nations high commissioner on refugees. Oakley said the United States, Vietnam and the U.N. office agreed "in principle" on this plan during last week's Geneva conference on Indochina refugees.

Oakley held out the possibility that U.S.-cartered planes might land in Vietnam, presumably at Tan Son Nhut airport, to bring out approved applicants bound for the United States.

State Department officials described the plan as a humanitarian rather than a political gesture. "This will not be an interest section. We will negotiate nothing with the Vietnamese" on the consular visits, an officials said. Technically the consular officers will be in Vietnam on temporary duty as part of a U.N. Delegation, according to the plan.

The United States and Vietnam have no formal diplomatic ties, although they have made frequent contact at the United Nations and elsewhere. Vietnam has been told there is no chance that the United States will agree to establish diplomatic relations under present circumstances, officials said.

The United States previously provided Vietnam with the names of about 5,000 people believed eligible to come to the United States as immigrants to join family members who have taken refuge here. So far only 29 people on the list have appeared to claim visas.

The plan to assist family reunification by dispatching American consular officers was among several tangible U.S. steps flowing out of the Geneva meeting. Both State Department officials and members of Congress described the results of the meeting in hopeful terms yesterday, although all took pains to say that the most crucial a unanswered question is the future performance of the Vietnamese.

Declaring himself "not as optimistic" as some reports, Rep. Lester L. Wolff (D-N.Y.), chairman of the House Foreign Affairs subcommittee on Asia and the Pacific, said Vietnamese officals told him at Geneva it would take two to eight months to exercise conrol over "illegal" departures. "We're going to continue to have boat people, I believe," he said.

Rep. Joel Pritchard (R-Wash.), who also was at Geneva, accused Vietnam of using the refugee flow for many purposes: to "get rid" of a potentially troublesome minority; to trade control of refugees for economic aid, in "a blackmail operation;" to dislocate neighboring states economically and politically; to gain some bargaining leverage with its current major-power enemy, the People's Republic of China.

At the State Department, Oakley told reporters that the United States remains interested in convening a meeting of the U.N. Security Council to consider "threats to peace and security" arising from Vietnam's handling of refugees as well as its invsion of Cambodia.

Vietnamese efforts to stop "illegal" departures may ease the pressure on Southeast Asian states, but this is not a sufficient step, Oakley said. He said it is "very important" that Vietnamese citizens be given choices other than reeducation camps or forced explusion, in keeping with basic human rights.

In another aspect of aid to refugees, the Defense Department announced that ships and aircraft of the Seventh Fleet have been ordered to "alter their routes as feasible" to spend more time in areas where "boat people" ae likely to be. Long-range patrol planes have begun looking for refugee boats and additional planes will soon be assigned to this duty, Pentagon officials said.