The door to Rep. Mark Udall's office opens at lunchtime yesterday, and 13 chattering reporters and cameramen stream in.

The Colorado Democrat gawks. "I wish I could get this kind of coverage on my own," he says.

Indeed, the journalistic pack -- from CNN, the New York Times, The Washington Post, the Associated Press and elsewhere -- is interested not in the congressman but in the three people sitting demurely in armchairs in his office: a computer worker, a temp and a non-practicing lawyer.

Individually, they are ordinary citizens and political unknowns. But collectively, they are the Denver Three -- a political sensation in Colorado that is causing agita to a White House that has bested far more sophisticated foes.

The Denver Three's quest: to learn the identity of the "Mystery Man" who, impersonating a Secret Service agent, forcibly removed them from a taxpayer-funded Social Security event with President Bush three months ago because of a "No More Blood for Oil" bumper sticker on one of their cars.

They and their attorneys have filed 10 freedom-of-information requests. They won support from eight of Colorado's nine members of Congress and persuaded lawmakers to send letters of protest to the White House and Secret Service. Working from a Denver coffee shop and from a loft apartment, they spend hours each day contacting reporters, producing almost daily news coverage and provoking questions at White House briefings. They have a Web site and bumper stickers, and they got a well-funded liberal group to send them to Washington. Now they're talking about public meetings and a lawsuit.

"Who was the Mystery Man who removed us from your Denver town hall event?" demands Karen Bauer, one of the Denver Three. Toting cell phone and Snapple, she is standing in front of the White House on Monday afternoon, reading a letter to Bush before a small knot of journalists and a large clump of tourists.

"It's unconscionable," adds co-conspirator Alex Young.

"It's un-American," submits Leslie Weise, the third member of the trio.

The three try to drop off letters hand-addressed to Bush and top aides. When the guard refuses to take the delivery, they drop the letters into a Pennsylvania Avenue mailbox -- cameras running -- and then sit down with a reporter at a Starbucks to discuss their unlikely stardom.

It started when the three got tickets to Bush's March 21 Social Security town hall meeting in Colorado. They flirted with protesting at the event and wore "Stop the Lies" T-shirts underneath their business attire. But Weise worried about getting arrested.

Even so, they were identified after they arrived as potential troublemakers, and then forcefully removed by a man who, they had been told, was a Secret Service agent. Only later did they learn that the man wasn't an agent at all. The Secret Service launched an investigation (it's a crime to impersonate a law enforcement official), and the agency and the White House have both learned the impostor's identity -- but they're not talking.

No matter. The Denver Three say, in a memo they're distributing, "ALL ARROWS POINT TO WHITE HOUSE."

The White House says that's bunk. But a series of similar events have left the administration vulnerable to such charges. In February, a Bush spokesman blamed an "overzealous volunteer" for a 42-person blacklist used at a Bush event in North Dakota. Complaints have also come this year from New Hampshire and Arizona, and during the campaign, event participants were once required to sign loyalty oaths for admission.

The Denver Three have won both sympathy and fame at home; thanks to that, both Democratic and Republican lawmakers from Colorado are fawning.

After their visit to the White House on Monday, their first meeting yesterday is with the chief of staff to Rep. Diana DeGette (D-Colo.). After the three leave, the congresswoman issues a statement demanding to know "who kicked three of my constituents out of a taxpayer-funded event."

They trek across the Capitol grounds to the office of Sen. Wayne Allard (R-Colo.). Fox News is playing, and there's a photo of Bush's inauguration on the wall -- not home turf for the Denver Three. But Chief of Staff Sean Conway is solicitous, taking notes and nodding. "I think they're entitled to some answers," Conway says after they leave.

Next stop is the office of Rep. Bob Beauprez (R-Colo.), where Chief of Staff Sean Murphy, behind closed doors, complains that they're making the issue partisan. But in public, it's all sympathy. "We regret that it happened to them," spokesman Jordan Stoick says.

The Denver Three hurry onward; they have four more offices to visit, and they're late for a news conference with Udall -- who has already written three letters demanding answers. "These three are tenacious," he says.

And in demand. Barely out of Udall's office, they get two more calls -- from House Minority Leader Nancy Pelosi (D-Calif.) and Senate Democratic Policy Committee Chairman Byron L. Dorgan (D-N.D.) -- asking to meet the famous threesome.