WASHINGTON (AP) — A massive spending bill to fund five Cabinet departments for the upcoming budget year is about to hit the Senate floor, giving senators a rare opportunity for open debate on legislation of any kind.

Maybe. The chamber easily advanced the measure on a 95-3 test vote, but a subsequent agreement for debate terms proved elusive Tuesday. Democrats controlling the Senate have for years followed their GOP predecessors in restricting the ability of the rank and file to offer amendments to legislation, under longstanding Senate traditions.

The hybrid $180 billion measure by Appropriations Committee Chairwoman Barbara Mikulski, D-Md., would fund the departments of Commerce, Justice, Transportation, Housing and Urban Development and Agriculture for the 2015 budget year beginning Oct. 1.

It would be the first opportunity in several years for senators to have extended debate and offer floor amendments to an annual appropriations bill, but it's not clear whether the bitterly divided chamber will rise to the occasion. Negotiations to bypass floor procedures and begin debate Tuesday evening failed to bear fruit.

Republicans are sure to try to force votes that would make politically endangered Democrats squirm. And if Democrats try to quash such opportunities, they could seem high-handed. But the debate also promises votes on substantive issues such as revising hours of operation rules for the trucking industry.

The measure comes as the annual appropriations season is entering overdrive and key players like Mikulski are trying to revive the powerful Appropriations panel, which has been disrespected by both House Speaker John Boehner, R-Ohio, and Senate Majority Leader Harry Reid, D-Nev., in recent years.

The House, meanwhile, takes up a $570 billion Pentagon funding measure Wednesday, hours after the House Appropriations Committee was set to approve a bipartisan measure funding the Energy Department, Army Corp of Engineers water projects and the Defense Department's nuclear weapons program.

But House subcommittee debate Wednesday on a measure slashing the Internal Revenue Service's budget promises to be far more partisan, as was last week's floor debate on the Agriculture Department's measure, which opened the door for school districts to opt out of healthier school lunch standards — a top priority of first lady Michele Obama.

The Senate panel gave initial approval to bipartisan bills funding foreign aid and energy and water programs. Senate Minority Leader Mitch McConnell, R-Ky., who serves on the panel but participates chiefly at high-profile moments, has signaled that later this week he'll press an amendment to block any Environmental Protection Agency rules on carbon emissions from existing power plants, a move that, if successful, promises to boost his standing in eastern Kentucky coal country. He's got a good shot at winning since several pro-coal Democrats populate the panel.

Such amendments allow lawmakers opportunities to weigh in on issues big and small. The Senate floor measure, for example, would boost grants to help communities ease backlogs of rape tests, ease House GOP cuts to Amtrak and transportation grants, and, under a bipartisan provision by Maine Republican Susan Collins, relax government rules aimed at keeping tired truckers off the road.

In a dysfunctional Congress, the annual appropriations process is often the only game in town.