The House Comerce Committee, already the scene of a lively contest for its health subcommittee chairmanship, now faces a fight for the chair of its key oversight and investigations subcommittee.

Rep. John Murphy (D-N.Y.), chairman of the House Merchant Marine Committee, one of its subcommittees and ad hoc committee on the Outer Continental Shelf, has announced he will challenge Rep. Bob Eckhardt (D-Tex.) for the Commerce subcommittee spot.

Eckhadt is a liberal who has battled the oil and gas industry, sponsored legislation regulating toxic chemicals, and generally champoined comsumer and environmental causes. Murphy is a supporter of the maritime industry and unions and has generally take pro-business stands in other areas.

Eckhardt, who has been running for the psot for weeks, is continuing to campaign from a hospital, where he is suffering from an infection following coronary bypas surgery. Eckhardt said yesterday he is "still pretty confident" of winning.

Eckhardt said he found Murphy's announcement "in the mail with a getwell note on the bottom. My immediate reaction is that... it's a pretty heavy assignment load he's trying to take on."

Murphy is on vacation in the Virgin Islands and could not be reached for comment. But in a letter to his 22 fellow Democrats on the Commerce Committee who will vote on subcommittee chairmanships, Murphy cited his service on three Commerce subcommittees -- transportation, energy and communications -- as qualifying him for the oversight chair.

Democratic caucus rules say the chairman of a full committee shall not be chairman of a legislative subcommittee of any other committee. But Murphy's staff aide, Art Kosatka, said since the Commerce subcommittee performs only oversight and does not handle legislation, it does not come under the rule.

However, one member of the Commerce Committee said he is checking with the House parliamentarian on whether that interpretation of the caucus rule is correct.

Asked about the burden Murphy is attempting to take on, Kosatka said his boss already carries the burden of serving on three Commerce subcommittees in addition to his othe work. He said Murphy would likely give up two or possibly three of those subcommittee if he was elected oversight chairman.

The oversight chair was vacated by the retirement of Rep. John Moss (D-Calif.), who used the subcommittee to look into everything from drug pricing and gas supplies to failures of regulatory agencies. Technically, almost everything in the broad jurisdiction of the Commerce Committee -- health, transportation, commerce, energy and communication -- is within the scope of the oversight subcommittee, along with all the agencies and departments dealing with those subjects.

The subcommittee was a bone of contention once before, in 1975, when the Watergate-year freshmen participated in a coup that wrested the chair from the full committee's chairman, Harley Staggers (D-W. Va.), and gave it to Moss.

Today more chairmanship fights are being waged within the Commerce Committee than throughout the rest of the House as a whole.

Rep. Henry Waxman (D-Calif.) and Rep. Richardson Preyer (D-N.C.) are vying for the chair of the health subcommittee, left vacant when Rep. Paul Rogers (D-Fla.) retired.

Rep. James Scheuer (D-N.Y.) is seeking the chair of the consumer protection subcommittee, which Eckhardt would have to give up if he is elected oversight chairman.

If Scheuer is not elected, Rep. Richard Ottinger (D-N.Y.) said he is interested in that post.

Rep. James Florio (D-N.J.) is seeking the transportation subcommittee chair being vacated by defeated Rep. Fred Rooney (D-Pa.).

A question hanging over all of them is what Rep. David Satterfield (D-Va.) will do. Satterfield is fifth in seniority on the full committee and could try for all the subcommittees. Defeated once in an attempt to chair a subcommittee, he is not saying what he will do this time.