Members of the House Ways and Means Committee, meeting yesterday for the first time in closed session to write an overhaul of the tax code, agreed on drafting procedures that will give them broad flexibility to offer amendments -- but that raise the possibility the bill-writing process will move slowly.

Committee members took no votes, except for the 27-to-2 decision to close the session, and said little about the specific provisions of President Reagan's sweeping tax proposal or the alternatives that will be offered by the committee staff next week.

The meeting came as House and Senate leaders agreed that the prospects for final passage of a tax measure this year are dim.

The most contentious discussion in the Ways and Means meeting came over whether each amendment to the plan must bring in the same amount of tax revenue as the current system does, to keep the bill from increasing the federal deficit.

Almost every member expressed an opinion during the 45 minutes or so the topic was debated, and committee Chairman Dan Rostenkowski (D-Ill.) decided in the end that all amendments must be "revenue-neutral": If they propose retaining a deduction now slated for oblivion, they also must include a provision raising taxes elsewhere.

Next Thursday, the panel will get its first look at the staff alternatives to various provisions of the Reagan plan, which would do away with numerous deductions while cutting income tax rates. The following week, members will begin intensive drafting, beginning with sections concerning individuals' taxes, that is expected to last through most of October.

Joseph K. Dowley, chief counsel for the committee, emphasized that the staff options -- worked out on a bipartisan basis -- will not necessarily reflect Rostenkowski's views. However, the basic working document, the one that will be subject to amendment during the writing process, will be the staff proposals, not the Reagan plan.

"That says to me the burden of proof will be on anyone who wants to do something different," said Rep. Willis Gradison (R-Ohio). "That proposal will be the one on the table."

The procedures agreed to yesterday will permit committee members to re-amend sections of the bill they had previously completed and to juggle revenue between the corporate and individual tax codes to "pay for" their amendments. While members will thus have a strong voice in the shaping of the tax package, Dowley and others said the members may want to tighten the rules later if they find they are proceeding too slowly.

Treasury Secretary James A. Baker III, Deputy Secretary Richard G. Darman and Assistant Secretary Ronald A. Pearlman also attended the closed Ways and Means session. At one point during the meeting, according to participants, Rostenkowski looked directly at Baker and said he wanted the legislation to bear the stamp of the Ways and Means Committee.