Two leading Southern moderates, Reps. Gillis Long (D-La.) and Charles Rose (D-N.C.), are running for caucus chairman, the fourth-ranked post in the House Democratic leadership.Third-term Rep. Matthew McHugh (D-N.Y.) is thinking of getting in but concedes he is already pretty late.

The caucus of all House Democrats was rejuvenated a decade ago and served as the vehicle for the basic procedural changes of recent years that broke the grip of the seniority system and opened up House proceedings. It has fallen into relative disuse recently as reform fervor receded and some members tried to use it to push pet legislative schemes often opposed by the leadership. The chairmanship comes open at the organization caucus in December when current Chairman Thomas Foley (D-Wash.) must step down after a second two-year term.

Rose and Long have very different ideas of what the function of the caucus should be. Rose, 41, and eight-year House member, thinks it should be used as a forum to discuss and try to achieve a party consensus on legislation. He has specialized in communications, helping lead the House into the computer age.

Long, 57 and a 10-year House member, thinks the caucus should stay away from legislation for fear it would lead to pressuring members into supporting positions they oppose. He thinks the caucus should focus on refining some of the procedural changes of the past decade, such as shrinking the proliferating number of subcommittees.

There are some undertones here of the fight between Reps. Richard Bolling (D-Mo.) and Phillip Burton (D.-Calif.) for majority leader four years ago, which ended in the election of Jim Wright (D.-Tex.). Long works closely with Bolling on the House Rules Committee. Rose managed Burton's campaign.

Long has been at work lining up votes longer than Rose and thinks he is ahead. He expects the position to go to the Southeast because the Northeast, Southwest and Midwest hold the top three leadership posts and the Far West has had the caucus chairmanship for the past eight years.