A congressional investigation has uncovered "numerous examples of extravagant" trips on luxury liners by federal employes traveling at taxpayer expense to and from overseas assignments, a House committee chairman says.

Rep. Jack Brooks (D-Tex.), head of the Government Operations Committee, said evidence of trips on ocean liners at prices several times the cost of equivalent airplane trips was turned up by a study begun last year by the General Accounting Office.

Copies of the GAO report have not been made public by the committee, but a source familiar with the document cited two examples it found of ocean liner travel by State Department personnel.

In one case, an official and his family, returning to Buenos Aires, Argentina, from home leave in Los Angeles, flew to Cartagena, Colombia, and then took a 25-day cruise to Buenos Aires, according to the source.

The source, who spoke on condition he not be identified, quoted the GAO as saying the voyage cost $18,156, compared with the $3,360 had the trip been made by air.

In the other case, an employe and his six dependents flew from New Delhi, India, for home leave in Spokane, Wash., and began the return trip by flying to New York. There they boarded the Queen Elizabeth II for a five-day crossing to England, where they took a flight back to India.

The cost of the ocean liner passage was $18,407, nearly four times the $4,732 for air fare from New York to England, the GAO reportedly found.

Brooks ordered the investigation in March 1984 after his committee held a hearing into the case of a U.S. Information Agency employe who took his family on a taxpayer-funded $17,371 trip up the Mississippi on the plush Delta Queen as he returned home from an assignment in South America.

The USIA said at the time that the riverboat ride was approved by the State Department, which handles travel arrangements for USIA.

Spokesmen for the State Department and USIA said there would be no comment until officials received copies of the GAO report. Executive Notes

*President Reagan yesterday appointed David A. Bockorny and J. Edward Fox as special assistants to work in the office that handles his relations with the House.

Bockorny has been on the staff of the National Association of Realtors since 1981, while Fox has worked as the principal deputy assistant secretary of State for legislation and intergovernmental affairs.

Reagan also appointed:

*Thomas F. Gibson III to be a special assistant to the president and director of public affairs. Gibson has worked as an aide for the White House Office of Cabinet Affairs.

*Susan K. Mathis to be a special assistant to the president and director of media relations. Mathis has worked served in the media relations office since 1981.

*Merlin Breaux to be a special assistant to the president for public liaison, in the area of economic issues. Breaux most recently served as vice president of industrial relations for Gulf Oil Corp.

*Agnes M. Waldron to be a special assistant to the president and director of research. Waldron worked as a staff member of the Senate Republican Policy Committee from 1977 to 1984.