ASPEN HILL, Md.

-- A man on a bus was shot in the chest and critically wounded early today, and a police task force was investigating as if it was related to the serial sniper who has killed nine people this month.

Police put a widespread dragnet into place immediately after the shooting, clogging traffic on Connecticut Avenue, one of the main arteries into Washington, D.C., just as the morning commute began.

The 40-year-old man was shot as he stood at the top of the steps of the bus, Montgomery County Police Capt. Nancy Demme said.

''We don't know if this is related but we're treating this as if it is,'' Demme said.

He was taken to Suburban Hospital in Bethesda, where Dr. Eugene Passamani said he was in critical condition.

The shooting happened shortly before 6 a.m. near an apartment building and wooded area along Connecticut Avenue. The location, some 15 miles north of downtown Washington, is near the sites of the first six sniper attacks, all on Oct. 2 and 3. In all, 12 people have been shot by the sniper in Maryland, Virginia and Washington, D.C.; three were critically wounded.

Agents for the federal Bureau of Alcohol, Tobacco and Firearms combed the area. A police dog searched near a basketball court in a park, and police helicopters flew over the scene.

On Monday, the hunt for the sniper turned into a case of high-stakes phone tag.

The most recent shooting blamed on the sniper critically wounded a 37-year-old man Saturday night outside a steakhouse in Ashland, Va. On Monday, police said they received a call about the attack, hinting it was from the sniper, but that the call was muddled.

''The person you called could not hear everything you said. The audio was unclear and we want to get it right. Call us back so that we can clearly understand,'' said Montgomery County Police Chief Charles Moose, who has been leading the hunt.

Schools in the Richmond area, near Saturday's shooting, remained closed a second day today.

Moose did not disclose who received the muddled phone call, when it was made or other details. But investigators believe the call may have come from the sniper and that the caller was the person who left a note and phone number at the scene of Saturday night's shooting, a law enforcement source told The Associated Press on condition of anonymity.

On Sunday, Moose publicly pleaded with the note writer to call authorities.

Then in the first of two televised statements Monday, he said: ''The message that needs to be delivered is that we are going to respond to a message that we have received. We are preparing our response at this time.''

Separate reports today shed more light on the message. The Los Angeles Times and Richmond Times-Dispatch said it contained a threat directed toward schools. Several news organizations reported that the killer demanded money.

The Los Angeles Times, citing unidentified federal agents, said the letter was ''very lengthy'' and poorly worded, bordering on broken English.

The victim shot Saturday night was felled by a single shot to the stomach. He remained in critical but stable condition at a Richmond hospital today after doctors removed his spleen and parts of his pancreas and stomach. Surgeons retrieved the bullet after surgery Sunday, and ballistics tests linked the slug to the ambush killer.

Moose's plea Monday came hours after Virginia authorities surrounded a white van parked near an Exxon gas station just outside Richmond and seized two men. They said later the men had no connection to the sniper.

Several newspapers reported Tuesday that the men apparently made the mistake of driving the white van up to a phone booth being watched by police. The phone booth had been traced to one that the letter writer had used.

A Justice Department official said deportation proceedings had begun against the two -- a 24-year-old Mexican and 35-year-old Guatemalan.

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Associated Press writers Bill Baskervill, Allen G. Breed, Ron Fournier and Pete Yost contributed to this report.