As the Senate Appropriations Committee prepares to appoint its subcommittee chairmen, one thing is already clear: Barbara A. Mikulski’s takeover of the full panel should be a boon to the National Security Agency, the largest of the U.S. intelligence agencies and one of the largest employers in her state of Maryland.

The NSA will have a fierce advocate for its budget in Mikulski, a fifth-term Democrat who has played a role in building the agency up in her home state. What is less clear is whether she will also exert much critical oversight of an agency that is often at the center of the most cutting-edge — and controversial — intelligence missions.

A spokeswoman for Mikulski said she could balance both advocacy and oversight.

“As both a member of the Intelligence Committee and a member of the Appropriations Committee, Senator Mikulski has a long history of making sure the National Security Agency has the resources it needs to meet its vital mission of protecting the nation,” said the spokeswoman, Rachel MacKnight. “At the same time, she has robustly fulfilled her oversight responsibility, helping to ensure Americans’ civil liberties and privacy are protected. That balance will continue as she takes on the role of Appropriations chairwoman.”

Mikulski could be in line to take the Defense Appropriations Subcommittee gavel as well, where she would have an even greater stake in deciding the NSA budget, since most intelligence community funding is tucked into the annual defense spending bill. A decision on that subcommittee could come as soon as Wednesday.

Either way, Mikulski will be in a position to influence how much Congress fills the agency’s coffers. Although the NSA budget is classified, NSA historian Matthew Aid said it was pegged at a high of nearly $10 billion in 2009. Like most federal agencies in recent years, the budget has dropped since.

The Maryland Angle

Having Mikulski’s hand on the till can only be a positive for the agency’s ambitions, though, said James Bamford, another NSA historian. When former Appropriations Chairman Daniel K. Inouye, D-Hawaii, died last year, it first looked like the shuffling of positions would put Mikulski in line for the Intelligence Committee gavel.

But she ended up with Appropriations, an outcome that Bamford and others said should work out better for the NSA.

“From NSA’s standpoint, they would rather have her at Appropriations than Intelligence, because they don’t seem to have any problems with the Intelligence Committee the way it is, not having any push back from the committee over the years,” said Bamford. “They don’t really need any help in getting legislation passed and laws and so forth. They would really appreciate having somebody that fights for more buildings and more infrastructure in Maryland.”

Jim Dyer, a former House Appropriations Committee clerk and staff director who is now a principal with the Podesta Group, said that while much has been made of the diminishing power of congressional appropriators, they still generally have more sway than authorizing committees like Intelligence.

“I believe it’s in the NSA’s interests to be where she is today, because at the end of the day it’s about resources,” Dyer said. “I don’t want to diminish the power of the Senate Intelligence Committee, which has a lot of things to do, but resources is not one of them. They want her to be the ultimate arbiter.”

Nonetheless, much of Mikulski’s work could be in defending the agency from greater cuts.

One past budget forecast, Aid said, concluded that the NSA would probably lose between 10 to 15 percent budget and the same portion of personnel — the agency employs an estimated 35,000 people, Aid said — by the end of the first term of the Obama administration.

That proved pessimistic, he said: “I don’t think they lost that much.” But in the next four years, barring a major national security breach, Aid said that the expectation is that the agency will go down to about 25,000 people and the budget would land somewhere in the vicinity of $6.5 to $7 billion.

Dyer was more skeptical that the NSA would be subjected to any serious cuts, regardless of who is chairing the Appropriations panel, given that it is a “mission-critical” agency.

Bamford said the agency does have a record of extravagant and wasteful spending in its recent past, such as on the failed data analysis program known as Trailblazer.

“NSA has just gotten huge amounts of money and Barbara Mikulski has been pushing for it all along,” he said. “Her track record isn’t very good for protecting taxpayer dollars because she’s out there like a salesman trying to get as much money from Congress as possible for NSA, but she hasn’t done much in terms of holding NSA up to accountability.”

Mikulski has pressed for the NSA to take on new cybersecurity missions and for the U.S. Cyber Command to be located in Fort Meade, the home of the NSA. Fort Meade is the top employer in Maryland, according to the state government. When counting the contractors who serve the NSA, its reach as an employer in Maryland expands further still.

In news releases, Mikulski frequently touts new buildings and projects she has sought and received funding for at the NSA. Although she voiced concerns about the warrantless surveillance program of the George W. Bush administration, she voted for the 2008 law (PL 110-261) that effectively authorized it and the recent extension (PL 112-238) of the law’s surveillance powers.

Mikulski is not the only Maryland lawmaker in a position of influence over the NSA. Rep. C.A. Dutch Ruppersberger is the top Democrat on the House Intelligence panel. His district includes the NSA’s headquarters at Fort Meade.