By Andy Sullivan

WASHINGTON (Reuters) - As Washington empties out for the holidays, a final budget fight will play out in the nearly empty Capitol building as congressional staffers parcel out more than $1 trillion to fund everything from cybersecurity to student loans.

Unlike the knock-down budget battles that paralyzed government for much of the year, this debate will largely take place within what one lobbyist calls a "cone of silence" with Republicans and Democrats aiming to minimize discord as they race to set spending levels for thousands of individual government programs.

It's a chance for Congress to demonstrate that it is capable of doing its job after two years in which lawmakers let the government run on automatic pilot when they weren't shutting it down or imposing indiscriminate spending cuts.

It has also touched off a lobbying blitz as defense contractors, hospitals, day-care providers and thousands of other groups push to maximize funding for the programs that affect them most directly.

Business groups will push to fund job-training programs, while advocates for the elderly will fight for increased Alzheimer's disease research and teachers' unions will argue to restore money that has been cut from education.

There may be only so much they can do to influence the process as lawmakers retreat into their chambers to write the complex spending legislation.

"They absolutely know what our priorities are," said Beth Felder, a lobbyist for Johns Hopkins University, the largest academic recipient of U.S. research money. "At this point I don't think their phones need to be ringing off the hook."

For some, it's a chance to restore funding that fell victim to across-the-board "sequester" cuts that took effect in March. For others, it's a chance to launch new initiatives that have been sidelined for years as Democrats and Republicans have opted to renew old spending plans through temporary "continuing resolutions," rather than write new ones.

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At Johns Hopkins, programs funded through the appropriations measures cover some hospital patients' medical bills and help students pay for their education. Researchers build satellites and develop missile-defense systems for the government and rely on federal money to fund medical research projects.

Federal spending is far and away the most important topic for lobbyists and their clients who hire them. Lobbying firms reported working on behalf of 3,076 clients this year for budget and spending issues, nearly twice as much as any other issue, according to the Center for Responsive Politics.

Collectively, those lobbyists can claim a partial victory. The budget deal that passed the House of Representatives and the Senate this week gives lawmakers authority to spend $45 billion more than would have otherwise been available.

RISING TIDE FOR INTEREST GROUPS

Now those interest groups will be essentially competing with each other for a slice of the same pie.

"We cooperate because a rising tide lifts all boats," said Emily Holubowich, who heads a coalition of 3,200 organizations that have pressed for more domestic funding. "Then we're competing with one another for those limited resources."

The deal provides a ceasefire in the budget wars that have consumed Washington since Republicans won control of the House in 2010 on a promise to cut spending.

It gives lawmakers on the appropriations committees $1.012 trillion to spend, splitting the difference between the House and the Democratic-controlled Senate.

It's not clear how that money will be divided.

Lobbyists say they expect it will be split evenly between military and domestic programs, with the money being distributed proportionately between the 12 subcommittees that each oversee a portion of the government.

But they're not likely to learn much more than that over the coming weeks as lawmakers will try to keep their work as private as possible, said Jim Dyer, a longtime Republican appropriations staffer who now works as a lobbyist.

"If a decision gets out, there'll be five people to preserve it and 10 people to overthrow it. You have to be very careful about the information that goes out in the public domain at this time," he said.

Congress hasn't written proper spending laws for most domestic programs since December 2011, opting instead to fund wide swaths of the government under continuing resolutions that freeze operations in place.

A CHANCE FOR NEW INITIATIVES

As a result, new initiatives have been put on hold.

Among them, for example, is a plan that would use advanced molecular-identification techniques to identify and isolate outbreaks of food poisoning, influenza or other public health threats more quickly.

Obama requested $40 million for the program this spring, and the Senate approved spending for half that amount in the summer.

Lobbyist Peter Kyriacopoulos brought in state and local public health workers to pitch the program to lawmakers in March, and he's following up with phone calls to staffers now. But he says it may be tough to convince Republicans to sign off on new spending.

"The House has been operating in a very unique way, so we go in and say what we can and we hope for the best," he said. "But no one's told me to go away," he said.

Others are more optimistic. Armed with figures that show how many patients in each congressional district have been unable to get treatment due to the sequester cuts, David Pugach of the American Cancer Society has been pressing appropriators to restore medical research funding at the National Institutes of Health to its pre-sequester level.

"When appropriators are making decisions based on what they say is most important, funding for cancer research and prevention should be at the top of that list and in all likelihood would do rather well," he said.

As the sequester forced sharp cutbacks in the Head Start early childhood education program, backers across the country ensured the cuts were covered in local media and pressured lawmakers to restore funding. Hopefully, that will have generated enough momentum to restore the $400 million that has been cut, said Yasmina Vinci of the National Head Start Association.

"Our first, biggest, most glaring priority is restoring the cuts that happened," she said. "I'm hoping we have done our work."

(Editing by Fred Barbash and Eric Walsh)