WASHINGTON -- Hoping to craft a set of rules changes that will have the support needed to get through the chamber, Senate Democrats have begun scaling back the reach of the legislation proposed by some of their caucus' staunchest filibuster-reform advocates.

Lawmakers are set to debate -- and possibly finalize -- recommendations during what promises to be a high-stakes caucus meeting Tuesday afternoon. The weekly lunch could set up an effort later that day to push reforms through on a straight up-or-down vote, but activists warned Monday morning that negotiations could be extended longer. Some Democrats are wary of exercising the so-called "constitutional option" -- which would allow them to set the chamber rules with just 50 votes -- pushing instead to settle for a smaller package of reforms capable of garnering the 67 votes needed for a midsession rules change.

In the past few days and weeks, Senate Rules Committee Chairman Chuck Schumer (D-N.Y.) and ranking Republican Lamar Alexander (Tenn.) have held talks on some of those measures. The result is less ambitious than the initial proposal, top Senate aides say, but more likely to attract GOP support.

Lawmakers have generally agreed that the Senate should eliminate the use of secret holds, which allow members to stop votes on nominations anonymously. They have also found some agreement on a deal that would limit the majority leader's ability to "fill the tree," a parliamentary maneuver to prevent the minority party from offering amendments, "in exchange for filibustering less," a senior aide said. There also appears to be an informal deal to reduce the number of judicial and executive-branch nominations requiring confirmation.

All of those elements are contained in a package that was introduced by Sens. Tom Udall (D-N.M.) and Jeff Merkley (D-Ore.) in early January. What are missing, according to the top aide, are the more far-reaching suggestions, including a proposal "guaranteeing post-cloture