The Pentagon briefing is proceeding crisply -- with praise for the "brilliant" war plan, videos of U.S. bombing hits, color-coded maps of coalition progress -- when the tone abruptly turns combative.

NBC's Jim Miklaszewski, noting that officials have confirmed just 28 American dead and 40 wounded, demands: "Is there any effort to either unreport or underreport casualties from the battlefield?"

"Oh my goodness. Now you know that wouldn't be the case," Defense Secretary Donald Rumsfeld says. Growing more agitated by the moment, he says: "That's just terrible to think that. Even to suggest it is outrageous. Most certainly not."

ABC's John McWethy strikes next, pointing out that no one has contradicted a lieutenant general who says the war will last longer than expected. "So is this an endorsement of plain-spoken assessment of your battlefield commanders when it may not necessarily agree with the perception that the administration has?"

"There's not some coordinated perception that's being peddled," Rumsfeld shoots back.

But the debate over the state of the war is, at bottom, a question of perception, and it is shaped in part by four veteran television reporters who patrol the corridors of this massive building. The M brigade -- Miklaszewski, McWethy, CBS's David Martin and CNN's Jamie McIntyre -- provides the daily scorecard for millions of viewers. And the Pentagon reporters, it turns out, are not the biggest fans of their embedded colleagues filing from the battlefield.

"I thought it was going to reduce me to irrelevance, but it doesn't," Martin says in his cramped cubbyhole, where he must close the door for privacy from the rival offices of NBC and ABC. "No one is out there with the big picture. I'm the big-picture guy."

The reporters usually maintain a sober, slightly harried air, not unlike the medal-wearing officials they cover. And, like a handful of their print counterparts, they have amassed a far-flung network of military sources over the years.

"Those long-term, trusting relationships pay off when the chips are down," says Miklaszewski, who began the first of several Pentagon tours in 1985.

The biggest change from previous conflicts is that the beat reporters are drowning in real-time information from Iraq, while Rumsfeld's department tends to be slow-moving and cautious. McWethy, who started as a television correspondent here in 1979, fingers a press release announcing that eight Marines are missing -- which news organizations have been reporting since the weekend before last. "Finally, five days later they're verifying this," he says.

While the embedded correspondents have furnished a "wonderful" portrait of the front lines, McWethy says, "they're horrible for a reporter operating at the seat of government because their information is so far ahead of what this bureaucracy is able to verify. The military guys at the Pentagon are frustrated because they know we are asking questions about things they won't know about through their channels for hours or days."

Martin recalls handing Rumsfeld a CBS report from the field, in the greenroom before an appearance on "Face the Nation," that Marines had been killed in a battle at Nasiriyah. "It was the first he'd heard of it," Martin says.

Martin, who assumed his post in 1983, quickly realized that "he may be secretary of defense, but that stuff's still got to go through the chain of command."

Says Miklaszewski: "It's not that people here at the Pentagon don't want to tell us. They can't tell us."

Pentagon spokeswoman Torie Clarke denies that she and her colleagues are frustrated by any lag in confirming news reports. "We try to strike a balance between the desire to get information out and the responsibility to be as accurate as possible," she says.

McIntyre, who set up shop here in 1992, sees his role as sifting through information from all sides in an effort to divine what the military calls ground truth.

"We thought the embedded reporters would be more accurate because they would be eyewitnesses," he says. "A lot of times, what we're learning from embedded reporters is what they've been told, what they've heard. But upon further checking, these reports don't always turn out to be what they seem."

Last week, McIntyre recalls, CNN's Walter Rodgers, traveling with the Army's 7th Cavalry, reported that the unit had detected a significant movement of Republican Guard forces heading in their direction. "As the day went on," McIntyre says, "it became clearer and clearer that there was no big column heading south."

A report that U.S. troops had found an Iraqi chemical weapons plant, which briefly got big play on cable before being knocked down, emanated from an embedded reporter for the Jerusalem Post.

For all their buttonholing of the brass, the M brigade's most important role is as military analysts. They have been through past wars, they know how to break the code, and they are skeptical of the official reassurances -- a view they don't hesitate to express.

"There's beginning to be a credibility gap between what officials here in the Pentagon are saying about the progress of the war and what commanders in the field are saying," Martin says on CBS.

The drive toward Baghdad "is stuck in the mud. It is stuck in the sand," McWethy says on ABC.

On NBC, Miklaszewski says: "Military sources say [that] when asked, Army Chief of Staff Erik Shinseki told President Bush the plan 'did not have enough ground troops.' "

"Privately," McIntyre says on CNN, "some Pentagon officials concede U.S. military planners may have underestimated the extent Saddam Hussein would use his Fedayeen fighters and other regime loyalists to launch guerrilla attacks against coalition forces and intimidate civilians."

No wonder Rumsfeld is complaining about "mood swings in the media" and "hyperventilating" critics.

While the field correspondents in helmets and military fatigues -- David Bloom, John Roberts, Ted Koppel, Oliver North -- are grabbing much of the spotlight, the Pentagon reporters, whose life work is scrutinizing the military, can sound a bit disdainful.

"Riding around in a tank is fun, but you don't know [expletive] about what's going on," McWethy says. The embedded journalists are providing a "soda straw view" of the war, flavorful but very narrow.

"Every night, I'm doing long, comprehensive, enormously demanding summary pieces," McWethy says. "Peter [Jennings] comes to me and I try to put the battlefield in perspective."

They've all wondered whether traveling with the troops would beat being stationed in Arlington -- but aren't all that tempted. "I know they're awake 20 hours a day, sleeping in the mud," Miklaszewski says. "I get enough adrenaline out of the Pentagon for the time being, thank you."

The pace can be brutal. Martin and McWethy service the morning and evening newscasts, with live shots in between when CBS and ABC break into regular programming. McIntyre, whose off-camera lower half is clad in jeans and sneakers, is on the air at least twice an hour (including CNN International), working with partner Barbara Starr on a shift that stretches from 11 a.m. to 11 p.m.

"CNN often wants to know about whatever has just happened," he says. "At some point we have to step back and say what do all these events tell us about what's going on."

Miklaszewski also provides updates for MSNBC and CNBC, and the cable demands force him to rely on his producer, Tammy Kupperman, for additional reporting. By evening he's popping up on the likes of "Dateline," "Hardball" and "The News With Brian Williams," making back-to-back appearances by flipping a switch on his desk.

"They all want a piece of you," he says. "That gets a little tiresome after a while, but it's great exposure."

Howard Kurtz hosts CNN's weekly media program.

At a Pentagon briefing, Defense Secretary Donald Rumsfeld walks by Jamie McIntyre (left), Bret Baier of Fox, John McWethy and Jim Miklaszewski. ABC's John McWethy, one of the four veteran TV reporters based at the Pentagon, contrasts his analysis with the "soda straw view" of the embeds.