WASHINGTON (AP) _ Kenneth J. Kies, chief of staff of the Joint Committee on Taxation, plans to leave the tax research panel by the end of the month, officials said Tuesday.

Kies, 46, spent three years as head of the panel, which provides research to both House and Senate tax writing committees. Scott Brenner, a spokesman for the House Ways and Means Committee, confirmed that Kies announced he will leave at the end of the month, but his future employment plans weren't known. Kies was expected to return to the private sector.

Senate Finance Committee Chairman William V. Roth Jr., R-Del., said the tax committees will have a busy agenda in the next two years and he intends to fill the vacancy quickly.

``I thank Ken for his hard work and dedication and wish him well in his future endeavors,'' Roth said in a statement.

Prior to joining the Joint Tax Committee, Kies was a lobbyist and tax lawyer in the Washington office of Baker & Hostetler, a Cleveland law firm. From 1982-87, Kies served as chief minority tax counsel for Rep. Bill Archer, R-Texas, then the ranking Republican on the committee.

During his tenure, Kies played a central role in passage of the 1997 Taxpayer Relief Act, the biggest tax cut passage by Congress in a decade.