The House Ethics Committee moved yesterday to begin its long-awaited investigation of South Korean influence buying in Congress by voting to ask for a $530,000 investigative budget - double last year's.

The committee voted, 5 to 4, against freshman a motion by Rep. Bruce Caputo (R-N.Y.) for an $875,000 budget request. Rep. Richardson Preyer (D-N.C.), who cast the vote to break a 4-4 tie, said he favored the lower figure because he had been "shell-shocked" by the recent furor over the House assassination committee's $6.5 million budget request.

The committee also voted yesterday to hire the law firm of former assistant Watergate special prosecutor Philip A. Locovara to head the inquiry.

An official vote on a resolution outlining the scope of the investigation was delayed because of the committee lost its quorum after a 1 1/2-hour executive session. Rep. John J. Flynt Jr. (D-Ga.), chairman of the committee, said after the meeting, however, that it's the unaminous feeling of the committee to proceed into an investigation of the so-called Korean matter." He said Lacovara would start questioning witnesses immediately, but he offered no timetable for concluding the investigation other than saying it would be "thorough and complete."

The committee has been considering such an inquiry since published reports last fall that South Korean President Park Chung Hee personally directed a massive lobbying efforts for U.S. aid by lavishing hundreds of thousands of dollars in cash and gifts on some members of Congress.