Air carrier with HTS TRACON at 4000; cleared for visual approach to Runway 30; was issued departure traffic and instructed to maintain visual separation; received TCAS RA; pilot flying elected not to comply with RA instruction.

Narrative

We were with Approach Control into HTS; at 4000 FT. Approach points out Air Carrier Y just departing off Runway 30 out of HTS we were given maintain visual separation and contact Tower. We asked are we cleared for the visual? He said 'yes; contact Tower.' We then noticed Air Carrier Y made a left climbing turn southward off Runway 30 right into our path. They were climbing and we were descending heading 160 degrees on a left downwind for Runway 30. They continued their turn and climb as we where descending and we got an RA to climb. The Captain decided a climb would (not) work since Air Carrier Y was climbing. I wanted to climb; but instead we slowed our descent and gently turned left as the other aircraft was approaching. We remained clear of traffic and as Air Carrier Y passed I saw they had just started a descent as part of their RA I suppose. If the Captain had followed the RA and climbed I think we would have had a much greater distance between the two aircraft; but it all happened so fast I couldn't verbalize my desire to follow the RA in time to suppress the Captain to do so. It was a deer in the headlights situation. We do not know what Air Carrier Y was cleared for; but it was to maintain visual. They should have waited to turn south after we passed as they were going the opposite direction than us before they turned; that would have worked just fine. I knew to follow what the RA says and I won't hesitate in the future to request it be done when it gets ignored by the flying pilot like it was this time. (Hopefully that won't happen again.) The Controller in HTS did not seen to control this traffic situation very well; but again; I don't know what Air Carrier Y was cleared for. I would have liked to know that Air Carrier Y was going to turn south in front of us.