The child of another Reagan administration Cabinet officer has landed a job at the U.S. International Communication Agency (ICA), the organization that handles the government's overseas press and cultural relations.

Barbara Haig, the 25-year-old daughter of Secretary of State Alexander M. Haig Jr., was hired last month as an $18,585-a-year staff assistant to the associate director of ICA's programs division in Washington.

In August, the 34-year-old son of Defense Secretary Caspar W. Weinberger set up shop in New York City in a $44,500-a-year job running ICA's public liaison office.

According to ICA officials, Haig was hired under "Schedule C," which normally applies to political appointees who are not career civil servants. These officials also said after checking with agency legal officers that "the law is clear" and that the Haig appointment does not violate various federal statutes dealing with nepotism--favoritism to relatives.

These statutes basically prohibit a government official from appointing or promoting "a relative in his or her agency or in an agency over which he exercises jurisdiction or control," according to officials in the Office of Personnel Management.

In the case of Weinberger's son, he is not working for the Defense Department and thus not in an agency over which his father has any control or jurisdiction.

As for the Haig appointment, ICA officials point out that theirs is "an independent agency, not part of the State Department." They acknowledge, however, that ICA "does take political guidance from the secretary of state and in practice there is a series of contacts and meetings" regularly between ICA officials and their counterparts at State.

The ICA activities abroad include exhibitions, television, magazine and film services and the Voice of America news broadcasting service.

Although ICA, like most other government agencies, is now under budgetary ceilings on employment and is trying to reduce from about 8,000 employes to less than 7,500, the agency is not technically under a hiring freeze. Officials say that Schedule C appointments are exempt from such freezes anyway.

Officially, Schedule C appointments are defined as involving "positions of a confidential or policy-determining character, excepted from the competitive service, to which appointments may be made without examination by the Office of Personnel Management."

When political appointees are named to top-level jobs, they normally require Senate confirmation. But there are many jobs, frequently for secretaries, chauffeurs and other assistants to the higher-level appointments, that also come under Schedule C jurisdiction, officials explain.

Hiring of relatives has been a sensitive matter in many administrations.