In a move that could be related to Carter administration efforts to tighten sanctions against Rhodesia, the Justice Department has been reviewing the lobbying activities of the Rhodesian Information Office in Washington.

Reliable sources said yesterday that the department's Criminal Division recently started scrutinizing the information office's conformity with the provisions of the Foreign Agents Registration Act. The sources added that a Criminal Division attorney and an FBI agent visited the office at 2852 McGill Terrace NW yesterday and began examining its records.

The Justice Department's action comes against a background of escalating support by the Carter administration for majority black rule in Rhodesia, a southern Africa republic where approximately 250,000 whites govern 5.5 million blacks.

As part of its pressure on Prime Minister Ian Smith's government, the United states is known to be supporting a pending United Nations resolution aimed at forcing the closure of offices maintained by Rhodesia in other countries.

Justice Department officials refused to comment yesterday on whether the Rhodesian office in Washington is under investigation. They also denied that their department might be acting in concert with the State Department and White House to find a legal pretext for closing the office.

These officials noted that the office, which is registered as an "agency" of a foreign power, must file reports of its activities and expenditures with the Justice Department every six months. The department, they added, could move against the office only if it detected some violation of the Foreign Agents Registration Act.

However, several reliable sources said they believed there is a connection between the Justice Department review and the State Department's support of the resolution that is expected to win adoption shortly by the U.N. Security Council.

The resolution would call on U.N. member nations to ban the transfer of Rhodesian funds within their borders - a step that would cut off Rhodesia's ability to finance the information office it maintains in Washington, Australia and France.

Some sources said they believed that the Justice Department's scrutiny of the Washington office might be aimed at preparing the way for such a ban, if and when the administration puts it in effort, by pinpointing the nature and source of funds used by the Rhodesian representatives here.

The office was established in February, 1966, following Rhodesia's 1965 declaration of independence from Britain. Before that, Rhodesia had maintained a diplomatic presence in Washington that was officially a part of the British embassy.

The office has been run since its inception by Kenneth H. Towsey, who previously had been the Smith government's "counselor for Rhodesian affairs" within the British embassy. Towsey is assisted by another Rhodesian national, H. J. C. Hooper, who deals primarily in information matters.

The office has no diplomatic or official status. Until now, however, the State Department, which cut the last diplomatic link to Rhodesia in 1970, has taken the position that there was no bar to its being in Washington as long as it conformed with the Foreign Agents Registration Act.

Towsey has functioned essentially as a lobbyist, attempting to win support for the Smith government's position through contacts with congressmen and private groups. The office also distributes literature about Rhodesia to a wide-ranging mailing list.