WASHINGTON — Transportation Security Administration screeners at Lambert-St. Louis International Airport probably wish that the fellow they chose to grill last March about a box of cash wasn’t a Ron Paul devotee who runs a committee devoted to individual rights and constitutional government.

But grill Steven Bierfeldt they did, and eight months later the incident has yielded revised rules requiring TSA agents to stick to matters related to flight security rather than policing airports for other crimes.

Bierfeldt and the American Civil Liberties Union, which represented him in a lawsuit, announced yesterday in a news release that the TSA had changed its rules in response to the litigation.

“It’s a huge victory for civil liberties that TSA agents no longer have free reign to conduct sweeping, baseless searches and detain passengers who don’t pose a threat to flight safety,” Bierfeldt said in a statement.

Bierfeldt said that he was ushered to a small room and questioned after passing a metal box containing $4,700 through a Lambert screening checkpoint. He said the cash related to his job as director of development for the Campaign for Liberty, a lobbying group that sprouted from the presidential campaign last year of Rep. Ron Paul, the Libertarian-Republican from Texas.

(Paul is scheduled to return Friday for an appearance in Iowa, where quadrennial precinct caucuses open the presidential election campaign season.)

Bierfeldt said that he was interrogated for a half-hour in an increasingly threatening manner and told that he was being placed under arrest. He recorded audio of the episode on his iPhone.

Bierfeldt’s suit contended that the TSA’s pre-flight screening should be aimed at keeping weapons and explosives off airplanes. Before it was due to be heard in September, the ACLU said the TSA issued a policy directive stating that “screening may not be conducted to detect evidence of crimes unrelated to transportation security.”

The government agency responded in October with a second directive pointing out that transporting large amounts of cash is not illegal, the release said. The ACLU added that it is taking steps to drop the suit on Bierfeldt’s behalf.

TSA was closed on this federal holiday and had not responded yet to a call seeking comment. A TSA blog post last spring defended the questioning but concluded that “language used by the TSA employee was inappropriate.”

A later blog post referring to “the St. Louis incident” says that “the tone and language used by the TSA employee was inappropriate and proper disciplinary action was taken.”