Yesterday was the kind of day cable news channels were made for: a day when speculation and chat could be largely ditched for the messy work of reporting on a real story - in this case, the arrest outside Frederick of two men believed responsible for the rash of sniper shootings in the suburbs of Washington.

National cable stations offered wall-to-wall coverage of the arrests in Maryland and related events in Tacoma, Wash., and Montgomery. Ala. Local channels did, too, dropping much of their regular schedule to carry continuous updates.

WJZ-TV's Denise Koch told viewers early yesterday afternoon to set their VCRs to the early-morning hours to tape pre-empted soap operas. She, like many of her peers, would be on the job for the long haul.

For cable channels, typical programming is often so much filler, relying upon discrete dispatches while news editors wait for a Big Story to latch onto and ride. There are a lot of pretenders to that title - the occasional three-alarm fire, highway car chase or stray shooting. Major stories, like shooting wars in Kashmir, the development of nukes in North Korea or even the multiple arson murders in Baltimore rate significant time, but not such blanket coverage.

Yesterday's news, heralding the possible end to the string of lethal shootings tying the Washington suburbs in knots, surely made the grade. But the coverage wasn't always pretty, as was shown yesterday morning when reporters shouted details over traffic on Interstate 70.

A frenzy accompanied much of the reporting on the air. John Allen Muhammad, 41, was arraigned yesterday on federal weapons charges; the 17-year-old, John Lee Malvo, taken into custody at the same time, was being held as a material witness. The older man was a U.S. gulf war veteran who was said to be a relatively recent convert to Islam.

Yet many things reported as the news broke had to be taken back over the course of the day. Many news outlets reported the two were stepfather and stepson. They weren't. CNN repeatedly said authorities had executed a search at a military-style training camp in Alabama linked to Islamic militants. They hadn't.

There had been equally awkward episodes before yesterday. Last weekend, for example, reporters pressed police officials about eyewitness accounts of olive-skinned men speeding away from the scene of a shooting outside Richmond.

But that question was based on an exchange overheard on a police scanner - typically too flimsy a basis to put on the air or in print. And, indeed, the account proved to be false. But because the question was raised during a news conference carried live, it was broadcast across the nation's airwaves.

This is the promise and the challenge of television news - the reporting is taking place even as the news is being presented to viewers.

Yet this imperfect process is preferable to the days of speculation required to sustain a cable channel's decision to dwell on a topic when there's no true news, such as those days when the sniper did not strike.

"I'm struck by how many predictions by experts were on the mark," CNN anchor Leon Harris said cheerfully yesterday.

Perhaps he is. It's not clear he should be.

Bo Dietl, a former New York City police detective with his own consulting firm (do any of these guys raise tomatoes in retirement?), seemingly led CNN viewers astray - though it should be noted the men have not been charged with the shootings, let alone convicted.

"I believe that they're young teen-aged kids that are involved," he said one day last week, and then, having reached that conclusion, careened quickly to another.

"There's a very good possibility that it has something to do with these silly video games. Doom is one where they teach them how to be snipers," Dietl said. "It is not going to turn out to be ex-military. It will probably turn out to be some young kids."

Retired Delta Force operative Eric Haney, a fellow CNN source, assured viewers "I don't believe that they're military, ex-military, or have ever had a connection with the military."

A few days later, on Oct. 17, Fox News's John Gibson pressed Sen. Richard Shelby, the Alabama Republican who heads the Senate Intelligence Committee, to acknowledge a possible tie between the sniper and al-Qaida. After Shelby said his "hunch" was that the sniper was a "home-grown terrorist," Gibson tried twice more.

"CIA Director George Tenet ... says al-Qaida has reconstituted, they are coming after us, they want to execute attacks," Gibson said. "You see it in Bali, you see it in Kuwait. Do you see it in suburban D.C.?"

Shelby didn't, despite Gibson's best efforts.

To give Harris his due, not all of the rampant speculation would appear to have been misguided. Haney, for instance, said he thought there were two people responsible for the shootings, which is certainly suggested by yesterday's arrests. Stuart Meyers, a former police sharpshooter interviewed by Fox News, also suggested there was a duo at work. The lead person, he said, "may have some prior military experience, definitely not sniping experience."

Yet with so much contradictory speculation consuming so much time, something was bound to be right. It was a relief when the so-called experts were careful enough to concede that they were basing their conclusions on guesswork.

Throughout the coverage of the sniper shootings, broadcast reporters have had their stamina, patience and sanity stretched. This may explain some of the choices made, such as ABC News' interviewing its own Washington-area correspondents about how they had changed their daily routines.

Less palatable, yesterday morning, was the preening of Perry Buffington, a sometime consultant for the FBI, on WMAR, as he explained his own tie to one of the victims.

"Linda Franklin, I have a connection with," he told viewers. The tie? He had recently spoken with a group of FBI agents, some of whom had worked with her or known her.

Thin gruel on a day so thick with hope - and real news.