Time is fast running out on the fiscal 2010 appropriations season.

With the end of the fiscal year just three months away and the House and Senate on vastly different timetables for passing spending bills, the clock is ticking on hopes that Congress can avoid a massive omnibus spending bill or a stop-gap measure.

The House has managed to stay on its tight schedule of passing all 12 bills before August, but the Senate has struggled to pass even a single appropriations bill. Aides and lawmakers say keeping spending bills moving through the Senate is key to returning appropriations to regular order — and avoiding an omnibus or continuing resolution.

The Senate will try to pick up its pace this week, with the likely passage of the legislative branch spending bill on Monday and the Homeland Security appropriations bill on deck. However, health care legislation and the confirmation of Supreme Court nominee Sonia Sotomayor are likely to quickly push spending bills to the backburner later this month.

“We will see,— a spokeswoman for Senate Majority Leader Harry Reid (D-Nev.) said of the outlook for additional appropriations bills in the coming weeks. “Things are still being worked out, but we will have a busy work period.—

Should the Senate only complete two spending bills before August recess, it would leave only four weeks in September to pass the remaining 10, not to mention conferencing them with the House.

“It’s an extraordinarily ambitious schedule,— said one former Democratic Appropriations staffer, who added that it’s highly likely one or more short-term continuing resolutions will be necessary in the fall. Key aides and lawmakers have suggested an omnibus spending measure may be inevitable, depending on the level of cooperation between the parties.

The biggest hurdle remains securing floor time in the Senate, which affords the minority party considerable procedural opportunities for slowing legislation.

This dilemma was on display before recess, when the Senate was unable to finish even the legislative branch bill — historically the least controversial of the annual appropriations measures — after a handful of GOP Senators demanded votes on their amendments.

By contrast, the House completed four fiscal 2010 spending bills before the July recess, despite last month’s GOP floor protest over the amendment process that culminated in a record-setting 53 roll-call votes in a single day.

In response, House Democrats have used the Rules Committee to limit amendments and other opportunities for procedural mischief by disgruntled Republicans. So far, that’s kept the chamber on track to pass the 12 spending bills before the August recess.

But that still leaves four weeks for the House to pass eight spending bills, including two of the toughest — the Labor, Health and Human Services, and Education bill and the Defense measure — tentatively scheduled to be taken up during the last two weeks of July.

One House GOP aide called it a heavy lift to finish all the spending bills before August but acknowledged it’s possible with rules that “crank down debate— on the floor.

This week, the House may consider as many as three spending bills, including the Agriculture, rural development and Food and Drug Administration measure, the State and Foreign Operations bill, and the military construction and Veterans Affairs spending bill.