Although he still won't say so publicly, Rep. Dan Rostenkowski (D-Ill.) reportedly has opted to become chairman of the Ways and Means Committee next year rather than take the third-raning leadership post of majority whip.

He has the luxury of choosing between the two powerful positions because he sits just behind incumbent chairman Al Ullman (D-Ore.) and Whip John Brademas (D-Ind.), both of whom were defeated.The whip is picked by the majority leader subject to the speaker's veto and both Speaker Thomas P., (Tip) O'Neill Jr. and Majority Leader Jim Wright (D-Tex.) have said Rostenkowski can have either job. The chairmanship of the tax-writing Ways and Means Committee is generally considered the most prestigious legislative position in the House. But Rostenkowski, whose style runs more to politics than the drudgery of rewriting the tax code, could still try to get back on the leadership ladder when O'Neill steps down.

With Rostenkowski heading Ways and Means, a leading candidate for whip would be Rep. Thomas Foley (D-Wash.), who is stepping down as Democratic Caucus chairman after the maximum four years' service. Foley, one of the most respected House members, would give the West a voice in the leadership.

The changes also open up the position of chief deputy whip, which Rostenkowski now holds and which is considered a part of the leadership. There has been talk of moving up one of the three regional deputy whips such as Rep. Bill Alexander (D-Ark.) or putting in a junior member such as second termer Richard Gephardt (D-Mo.), a protege of Rules Committee Chairman Richard Bolling (D-Mo.).

Rep. Gillis Long (D-La.) is favored in a three-man race to succeed Foley as caucus chairman. Democrats will elect leaders for the next Congress at a caucus next week. O'Neill and Wright have no opposition.