Daniel Rosenbaum for The New York Times

Albert A. Foer, the president of the American Antitrust Institute, was enjoying a restful Sunday last March when news broke that AT&T was seeking to buy T-Mobile USA.

Dismayed by the possible blockbuster cellphone merger, Mr. Foer rushed to the institute’s global headquarters — the first-floor study of his Washington home — and swung into action.

He complained to a reporter that “AT&T was broken up and now it’s back with a vengeance.” In the ensuing weeks, his organization would send a letter to the Senate, submit a lengthy objection to the Federal Communications Commission and issue a 38-page white paper arguing that the merger would “result in higher prices, lower quality, less innovation and fewer choices for consumers and businesses.”

Faced with fierce opposition from the Obama administration, the two companies scrapped their $39 billion deal on Tuesday, handing Mr. Foer and his fellow antitrust-enforcement advocates a major victory.

“Of course we can’t claim credit for putting an end to the merger,” said Robert H. Lande, a director at the institute and a law professor at the University of Baltimore. “But we did our part, and this was a wonderful demonstration of how the system sometimes works exactly the way it is supposed to work.”

In a city swarming with corporate lobbyists and business interests, the American Antitrust Institute is a rare species. The nonprofit group argues for more vigilant enforcement of the antitrust laws, fighting mergers that it believes harm competition and countering the evils of cartels.

Since its inception in 1998, the organization has largely operated in an environment of lax antitrust regulation. The Bush administration is considered to have had a weak record in policing mergers and bringing monopolization cases. And courts over the last decade have generally cut back on the scope of antitrust liability.

But with the government’s opposition to the AT&T-T Mobile deal and investigations like the one into Google’s business practices, the Obama administration appears to be reinvigorating antitrust enforcement.

“We’ve been paying defensive ball the entire time,” Mr. Foer said. “It’s nice to see a bit of a momentum shift.”

Despite its grandiose name, the American Antitrust Institute is nothing more than a virtual network of 120 competition-policy experts around the globe. The organization’s tools are somewhat limited. It submits friend-of-the-court filings in legal cases, called amicus briefs; publishes papers and book-length treatises; and hosts symposiums on arcane topics like multichannel distribution in the Internet age.

The institute’s secret weapon is Mr. Foer, an indefatigable 67-year-old lawyer with a broad, gap-toothed smile who speaks about tying arrangements and predatory pricing the way most people discuss football and reality TV.

“A lot of Bert’s antitrust opinions are annoying,” said R. Hewitt Pate, the general counsel of Chevron and a former senior antitrust official in the Bush administration. “You disagree with him on the substance but you enjoy hanging out with him, and there are not enough people in Washington like that.”

While well known in antitrust circles, Mr. Foer is not nearly as famous as his children. He and his wife, Esther Safran Foer, are the parents of three accomplished writer sons.

There is Franklin, 37, a former editor of The New Republic who is at work on a book about American liberalism; Jonathan, 32, whose novel, “Extremely Loud and Incredibly Close,” is the basis for a Warner Brothers movie set for a Christmas release; and Joshua, 29, a winner of the National Memory Championships and whose book about the science of memory, “Moonwalking With Einstein,” was among this year’s most acclaimed nonfiction books.

Though a proud father — interviewed last week, he was still beaming from having attended the “Extremely Loud” premiere the night before — Mr. Foer is reticent to discuss his children.

“What I’ll say is that you can screw up your kids,” he said. “And that’s our achievement — we didn’t screw them up.”

Mr. Foer’s interest in antitrust was piqued at the University of Chicago Law School, where he studied under Richard A. Posner and Ronald H. Coase, two leading scholars who promoted a laissez-faire approach to economics that is suspicious of government involvement.

“And I’ve been criticizing the Chicago School ever since,” Mr. Foer said.

After three years at the law firm Hogan & Hartson, Mr. Foer joined the Federal Trade Commission’s Bureau of Competition. He spent six years there, largely working on policy issues.

In 1983, while back in private practice, Mr. Foer’s legal career took a detour. His father had a heart attack, rendering him unable to run the family business, Melart Jewelers. Mr. Foer took over the 15-store Washington-area chain. He ran it for 13 years, and with the company struggling in the mid-’90s, Mr. Foer sold it to a competitor in a fire sale.

“Was I passionate about jewelry?” Mr. Foer said. “No, and that was my failing.”

At 50, Mr. Foer had to find a job. After casting about for several years, he returned to antitrust. At the time, although the government was bearing down on Microsoft’s monopolistic power, Mr. Foer saw the need for an organization that would pressure the government to toughen its antitrust stance.

A friend introduced him to Ralph Nader, the consumer rights activist, who encouraged Mr. Foer and helped him get his idea off the ground. A major hurdle was raising money, but Mr. Foer soon discovered that certain companies wanted to help him.

“There are always two sides in an antitrust case, and one is normally aligned with consumers,” he said. “That side ended up giving us money.”

Oracle, which was waging war with Microsoft, wrote the organization one of its first significant checks. A few years later, when the online travel service Orbitz was the subject of an antitrust inquiry, its competitor, Travelocity, gave the institute financial support.

Another source of financing comes from judges distributing unclaimed money from antitrust class-action settlements. The organization has received several million dollars under a legal doctrine called cy pres, which allows courts to dispense leftover cash in class-action lawsuits to benefit public interest programs.

Last month, it received about $900,000 from the settlement fund of an antitrust litigation against the credit card companies.

Today, the American Antitrust Institute runs on a budget of less than $1 million a year. Including Mr. Foer, five people are on the payroll, all of them working out of their homes, from Boston to Boulder. They pay themselves “good civil service salaries,” Mr. Foer said.

Even with the government’s recent stepped-up efforts in antitrust, Mr. Foer and his colleagues haven’t let up. This week, Diana Moss, the group’s senior research fellow, wrote an opinion article arguing that a proposal by Delta and US Airways to swap landing slots at New York and Washington airports put consumers at risk for higher fares. Last month, it urged the F.T.C. to block the merger between Express Scripts and Medco Health Solutions.

“At its root, antitrust is about human dignity and making sure consumers have a range of choices,” Mr. Foer said.

His son Frank said that he had realized ever since he was a child that antitrust was the defining passion of his father’s life. That notion came to the fore this year when he visited his father in a hospital recovery room after an operation. He was just waking up from anesthesia.

“We got the bastards,” Mr. Foer said groggily.

His family looked at one another, perplexed, and asked what he was talking about.

“I was just in the middle of an antitrust proceeding and we got the bastards,” he said.

The moment, said Frank, perfectly expressed his father’s id.

“The guy’s just coming out of surgery, and he’s not thinking about his wife and children,” Frank said. “He’s thinking about antitrust.”