A lobbyist hears from “very credible sources” that the White House is going to reverse a major health-care proposal. He tells a client in an e-mail, and that person then tells his own clients in a research note.

It sounds like the game of telephone that lobbyists, government officials and even reporters are drawn into every day in Washington. Except in this case, the chain of information may have triggered a spike in trades on Wall Street — and has now led to a government investigation into possible insider trading.

How the lobbyist, who works at the law firm Greenberg Traurig, stepped into this morass offers a window into what has become a routine and profitable practice at law firms and lobbying shops: In addition to their usual work, lobbyists share with financial firms the latest political tidbits they are gathering from sources, sending an e-mail here and there with the latest “political intelligence.” The financial firms value the information because it can inform their investments.

Recent attention has focused on a new breed of companies that offer political intelligence exclusively for investor clients, but some of the country’s most prominent law firms have gotten into the business, too.

The latest investigation has put an unwelcome spotlight on Greenberg Traurig, one of the country’s biggest law firms — and also known for having weathered the controversy surrounding one of its top lobbyists, Jack Abramoff, who was sentenced to prison for his part in a wide-ranging corruption scandal in 2006.

Greenberg Traurig was not doing anything unusual for a law firm by sharing political insight with clients who have investment interests. But when that information then informs stock trading, the ethics can become murky.

“The road to hell in this particular situation is not paved with clarity,” said Stephen M. Ryan, head of the government strategies practice group at the law firm McDermott Will & Emery. “You wander into it.”

The information being exchanged can quickly become explosive.

The brokerage firm Height Securities, which sells its analysis to hedge funds, said it wanted help staying on top of regulatory developments. So it hired Greenberg Traurig, whose lobbyist Mark Hayes had spent several years as an aide to Sen. Charles E. Grassley (R-Iowa) specializing in health care.

On April 1, according to e-mails obtained by The Washington Post, Height analyst Justin Simon had a question for Hayes: Was the White House about to reverse its stance on a critical Medicare policy?

Within minutes, Hayes confirmed it: “Our intel is the deal was already hatched.” Hayes explained that the Obama administration would increase funding for the Medicare Advantage program in exchange for Sen. Orrin G. Hatch’s support for an Obama appointee.

Simon sent out an alert to Height’s hundreds of investor clients — ahead of the administration’s public announcement — and trading in Humana, Aetna and other health-care stocks immediately soared.

Meanwhile, the text of Hayes’s e-mail was also spreading, pinning him as the direct source for the Height alert.

Hayes fired off an angry e-mail to Simon the next morning: “Very bad. I have a lot of damage control to do on multiple fronts because of this.”

A remorseful Simon apologized. “There is nothing I can say to describe the level of embarrassment and remorse I feel over the situation,” wrote Simon, who has since been subpoenaed by the government. “I will not be able to sleep over it tonight.”

Hayes’s attorney could not be reached for comment; an attorney for Simon declined to comment for the record. The chain of events was reported by the Wall Street Journal in April; the federal government then started issuing subpoenas.

Greenberg Traurig spokeswoman Jill Perry said the firm will no longer work with firms such as Height Securities that it considers part of the “political intelligence area,” explaining that doing so “may lead to misunderstanding and unintended use of those services.”

Adam Goldberg, a Height spokesman, disputed that characterization, saying his company “does not understand why Greenberg Traurig, a law and lobbying firm employing former government officials, would seek to label Height as a political intelligence firm.” Goldberg said Height was billed less than $5,000 by Greenberg Traurig.

Greenberg Traurig declined to comment on whether it also feeds information to other clients that are financial firms, in effect acting as a political intelligence firm itself (although Greenberg Traurig says it does not trade on any of the information it shares with clients).

Insider-trading laws say any information that is material — that is, it can move markets — and that is not public has to be handled very carefully, or there can be criminal charges. But determining which information rises to that level of sensitivity can be difficult. And there is no controlling what clients will do once they have the information.

Ryan, the lawyer at McDermott Will & Emery, describes the distinction this way: “If you take all the data points and you make a prediction and people trade on that prediction, it’s perfectly okay. All they’re doing is using the best intelligence available.”

But, he said, if you have actual information that there is an imminent government action, because you have talked with someone with direct, confidential knowledge, that crosses the line.

“It’s a potentially incestuous situation,” Ryan said, “because you may represent a hedge fund and do work for them, and then they say, ‘Wait a second. Isn’t your guy a real expert on that? Can you talk to the real expert in your firm?’ ”

Law firms, including Greenberg Traurig, frequently have intense ethics training. Legal observers said the firm had moved well past the Abramoff scandal, which they said did not reflect the firm’s intrinsic culture.

Perry, the Greenberg Traurig spokeswoman, said the firm has not found any indication that “any of our shareholders had access to any material confidential government information.”

Lobbying records show that Greenberg’s lobbying activity is down significantly from its heyday during the Abramoff era. The firm reported about $980,000 in lobbying revenue during 2013’s first quarter, a pace of less than $4 million for the year.

Greenberg’s biggest lobbying client during this period, by far, was Rational Entertainment Services, an Internet poker provider based on the Isle of Man, a tax haven in the Irish Sea known for its strict financial secrecy laws.

Greenberg’s other lobbying activity in the first quarter included extensive lobbying on Medicare, Medicaid and other health-care issues. Among its health-care clients was Humana, which paid Greenberg $10,000 to lobby on health-care legislation and topics such as the Medicare Advantage program, records show. Humana terminated its contract with Greenberg after the federal investigation came to light, according to public records.

Given how many law firms have gotten into the business of offering political analysis to investor clients, Ryan is not surprised to see an investigation such as this emerge.

“There’s been a rocket engine on the back of this thing,” said Ryan, adding that activity has particularly picked up in the past 10 years. “I always knew this day would come. I always knew there would be a case like this.”

Dina ElBoghdady and Tom Hamburger contributed to this report.