WASHINGTON — The financial firepower that fueled the rise of a network of conservative advocacy groups now pummeling Democrats with television ads can be traced, in part, to Box 72465 in the Boulder Hills post office, on a desert road on the northern outskirts of Phoenix.

That’s the address for the Center to Protect Patient Rights, an organization with ties to Charles and David H. Koch, the billionaire brothers who bankroll a number of conservative organizations.

During the 2010 midterm election, the center sent more than $55 million to 26 GOP-allied groups, tax filings show, funding opaque outfits such as American Future Fund, 60 Plus and Americans for Job Security that were behind a coordinated campaign against Democratic congressional candidates.

INTERACTIVE: The money behind the air war

The money from the center provided a sizable share of the war chest for those attacks, which included mailers in California, robo-calls in Florida and TV ads that inundated a pocket of northeastern Iowa. The organizations it financed poured at least $46 million into election-related communications in the 2010 cycle, among other expenditures.

In that campaign, outside groups — the vast majority backing Republicans — reported spending a record $304 million, according to the nonpartisan Center for Responsive Politics. Democratic-allied groups are still trying to match their success.

With such spending set to reach unprecedented levels in the 2012 election, the activities of the Center to Protect Patient Rights — whose existence was first reported this month by the Center for Responsive Politics — provide a glimpse into the network of deep-pocketed conservative advocacy groups that have already begun an air war against President Obama.

SPREADSHEET: Center to Protect Patient Rights grantees

Because these nonprofit groups are under no obligation to reveal their donors, the sources of their funding has remained a mystery.

The Koch brothers, with a combined net worth estimated by Forbes at $50 billion, are thought to be among the most generous backers of the efforts on the right. They have supported Americans for Prosperity, which, together with its sister foundation, plans to spend $151 million in the 2012 election.

Exactly how the Kochs and their allies are directing their sizable resources is unknown. But an examination of the Center to Protect Patient Rights provides some important clues.

The Kochs have several ties to the center. It is run by Sean Noble, a Phoenix-based GOP consultant who is a key operative in the Kochs’ political activities, as first noted by the investigative blog Republic Report. One of the center’s original directors, Heather Higgins, is chairwoman of the Independent Women’s Forum, which has received funding from a Koch-controlled foundation. And Cheryl Hillen, a Connecticut-based consultant who raised $2.6 million for the center, was director of fundraising for the Koch-backed Citizens for a Sound Economy.

Koch spokeswoman Melissa Cohlmia directed questions to the center, declining to say whether the Kochs were involved.

“Koch respects the lawful right of this organization, and others like it, to protect their privacy,” she said in an emailed statement.

The center was largely used as a vehicle to pass millions to other organizations, which also zealously guard the anonymity of their donors. Some campaign finance experts suggested the center could have been set up to pool money from various sources.

“Rather than have to make the decision yourself, you would entrust them to spread it around,” said Ellen P. Aprill, a tax law professor at Loyola Law School.

The center’s plans for 2012 are unknown. But in March, Noble filed paperwork expanding its advocacy beyond patient rights to include “limited government and free enterprise.”

Aside from its ties to the Kochs, there is scant evidence of who is behind the group. And no one involved would talk about it.

Noble did not respond to repeated phone calls and emails. Courtney Koshar, a Phoenix anesthesiologist and the organization’s only other director, did not respond to requests for comment. And a Phoenix doctor who once sat on its board said he couldn’t remember who asked him to join.

“I honestly played very little role,” said Dr. Eric Novack, who headed an organization called the US Health Freedom Coalition that received nearly its entire budget — $1.7 million — from the center to help pass a state ballot measure that aimed to block President Obama’s healthcare overhaul.

“This is a classic example of how our campaign finance system has entirely fallen apart,” said Craig Holman, lobbyist for Public Citizen, which advocates stricter campaign finance rules. “We really don’t know where this money originated from.”

The Center to Protect Patient Rights was created in April 2009, just as the debate over the healthcare bill was heating up. The group’s mission was to “protect the rights of patients to choose and use medical care providers,” according to its corporate paperwork, filed in Maryland.

While never surfacing publicly, the center sent more than $10 million in its first year to groups such as Americans for Prosperity, which took a lead in protesting the measure.

“I think they saw what we were doing and liked it,” said Tim Phillips, president of Americans for Prosperity, which got $4.1 million. He said he did not know the source of the center’s funding and declined to comment on whether it still supports his group.

The center’s influence extended beyond the healthcare debate, tax filings show. Money also went to antiabortion groups such as the Susan B. Anthony List and to Americans for Tax Reform, led by Grover Norquist. In Florida, the center backed Protect Your Vote, a Republican effort to defeat two redistricting measures.

The largest share of the center’s money went to American Future Fund, a Des Moines-based group started by onetime GOP congressional aide Nick Ryan. The fund, which ran campaigns against two dozen Democrats in the 2010 election cycle, spent $23 million that period, tax filings show, with nearly $13 million coming from the center.

Its biggest target was an up-and-coming Iowa Democrat, Rep. Bruce Braley. In August 2010, American Future Fund launched an ad falsely claiming that Braley supported building a mosque at the former World Trade Center site in New York — the beginning of a $2-million fusillade that included radio ads, robo-calls and nine mailers.

“It was almost a feeling of helplessness because there was no way to identify who the source of the funds was,” Braley said.

After winning his 2008 race by 29 percentage points, Braley squeaked to a 2-percentage-point victory.

Knowing now who helped finance the attacks is small consolation, he said. “It does nothing to shed light on who is contributing the hundreds of millions now that is being wound up to be used in races like mine again,” he said.

Ryan did not respond to requests for comment.

The center appears closely linked with DCI Group, a Washington-based consulting firm that specializes in under-the-radar corporate campaigns.

At least five groups that received large grants from the center paid more than $9 million in services to DCI Group or Direct Response, a mail and phone-bank company. The two companies share a suite in a Phoenix office building, but a spokesman said they were no longer legally affiliated.

For example, the center gave more than $2 million to the similarly named Coalition to Protect Patients’ Rights, a Virginia-based nonprofit formed in spring 2009, five weeks after the center. The two organizations share the same Phoenix accountant and records custodian — both former DCI employees, according to their online resumes.

The coalition staged rallies in 2009 to lobby against the so-called public option, a government medical insurance proposal eventually dropped by the Obama administration. The center provided 80% of the coalition’s budget; nearly all went to DCI and Direct Response for consulting and voter contact.

DCI Group spokesman Craig Stevens said the firm did not set up the center or know where the coalition got its money.

New Orleans surgeon Donald Palmisano, former president of the American Medical Assn.and the public face of the coalition, also said he did not know the source of funding.

“I’m just the spokesperson,” Palmisano said.

matea.gold@latimes.com

joseph.tanfani@latimes.com

Special correspondent Matthew Trotter in Phoenix contributed to this report.