The Civil Service Commission is expected to pay a top Washington law firm in the neighborhood of $150,000 over the next six months to investigate the Civil Service Commission.

In November, CSC - the government's guardian of the federal merit system - hired the firm of Rogovin, Stern and Huge. Purpose is to conduct an in-depth investigation into charges that CSC itself has been guilty in the past of Violating merit rules, of discrimination, and of helping White House and Capitol Hill politicians channel unqualified friends into lifetime civil service jobs.

Mitchell Rogovin, who is heading the probe, is a former assistant attorney general. He represented the CIA during the congressional hearings into the intelligence community.

When CSC announced its decision to call in the respected legal firm, both parties declined to say how much it would cost.

Officials now confirm that the maximum outlay will be $150,000, broken down this way Senior advisors of the firm will bill the government $90 per hour; associates $60, and investigators and paralegals will get $20.CSC said travel cost also would be paid members of the firm if, as expected, their investigation takes them out of town to visit present and former CSC employees.

Commission workers will testify under oath, but former employees and persons not working for the government cannot be required to do so officials warn, however, that anyone refusing to aid in the Rogovin inquiries will certainly get a prominent mention in the final report, including explanations of what investigators wanted to know, why and why the individuals refused to answer.

Some old-timers at CSC are hoping the main focus of the inquiry will be into allegations that the agency has violated the rules it is supposed to enforce for others, and has been guilty of sex and race discrimination. That should be relatively painless for CSC's new team, since most of the alleged wrong-doing occurred before they joined the agency.

But the probe into alledge merit system abuses some of which have been well-documented not fully explained - could embarrass many people still working for the government, or still around town. Among those who might be stung by the findings are key members of the House Post Office-Civil Service Committee who were never shy - Democrats and Republicans alike - in asking CSC to bend some rules to find jobs for friends and constitutients. The Rogovin investigation won't knock the Korean CIA probe off the front pages very often. But it has an almost equally large number of people worried.