RICHFORD, VT., OCT. 28 -- Two men of apparent Lebanese descent, charged with conspiring to smuggle explosives into the United States from Canada, were denied bail today after a prosecutor described the bomb that investigators believe one of them carried across the border.

"If you transport an explosive device, you're up to no good," U.S. Magistrate Jerome J. Niedermeier said.

Niedermeier ordered Walid Nicolas Kabbani, 30, and Walid Majib Mourad, 38, held for trial. He postponed until Friday a bail hearing for a third man charged in the conspiracy, Georges Fouad Nicolas Younan, 44, who was unable to obtain a lawyer. Kabbani also is charged with entering the United States illegally.

All three men have identified themselves as Canadian citizens living in the Montreal area and are believed to be natives of Lebanon. They were arrested by U.S. Border Patrol officials last weekend after arousing the suspicions of the one-man police force here in Richford, population 1,500.

Prosecutors said today that they do not know why the explosive device was brought into the United States, but they are investigating the possibility that it was to be used in a terrorist attack.

At a news conference after today's hearing, U.S. Attorney George J. Terwilliger III said a black hood found with the bomb and bomb-making equipment resembled hoods used in terrorist attacks in the Middle East.

"It was not an ordinary ski mask," he said. "It was a nylon hood that would come down to shoulder length with an oval opening." Terwilliger said the bomb was made from two metal canisters filled with smokeless gunpowder and was powerful enough to puncture "the skin of an aircraft."

Terwilliger said that an investigation by the Royal Canadian Mounted Police indicated that Younan recently had bought gunpowder of the type in the bomb and that Kabbani had bought a pair of wirecutters identical to those found with the device.

According to the Federal Bureau of Investigation, Mourad and Younan crossed into the United States Friday evening near Richford, an isolated border town, telling border officials they were on their way to Boston for a holiday weekend. Affidavits filed by the Border Patrol indicate that an electronic sensor was set off less than an hour later by someone crossing the border at an illegal point.

The affidavits said boot prints later found in the area appeared to match the "distinctive pattern" of boots worn by Kabbani.

Richard Jewett, Richford's only police officer, spotted Kabbani on foot during "a routine patrol" Friday.

Jewett, 38, has lived in the area all his life and says it is not difficult to spot an outsider. "It's kind of a sixth sense," he said. "The fellow didn't look particularly different from anyone else. I guess it was something in the way he moved and the way he looked around."

Jewett said Kabbani appeared to be carrying a black knapsack. Nearby, Jewett said, he saw a silver van parked in a "No Trespassing" area and asked the two men inside to move the vehicle. They asked for directions to Burlington, an hour's drive away. It was about 10:15 p.m.

As he continued his patrol, Jewett saw Kabbani again, this time without his pack, and asked why he was walking the streets so late. Jewett said Kabbani replied that he was on his way back to Canada after a day of shopping in Burlington. When Jewett offered to drive him the rest of the way to the border, Kabbani accepted.

He left Kabbani with border officials, returned to town and saw the van in its new parking place, then watched as it pulled into a motel lot. This time, he said, he called the Border Patrol and kept the van in sight until border officials arrived.

At that point, Jewett grabbed his flashlight and searched for the knapsack he had seen Kabbani wearing. He found it about a mile from the motel, near where he first saw Kabbani, in grass on the roadside.

Jewett said he suspected that the pack contained drugs. "That's the usual thing that comes across the border," he said. He drove the package back to the border, a few miles away, so he could open it in the presence of Border Patrol officials.

Jewett said his first reaction, upon finding a bomb, was "unprintable." Then, he said, he realized that the bomb was sitting on the hood of his town's only police cruiser. "I sure didn't want to have to buy another one," he said.

Meanwhile, Border Patrol officials waited for morning and arrested Mourad and Younan as they returned to their van. Terwilliger said in a statement Monday that a search of the van revealed a soldering iron wrapped with wire identical to that found on the bomb in the bag.

An application for a search warrant for the van was dated Tuesday. It was unknown whether verbal authorization to search was issued earlier by phone.

Federal law enforcement sources said today they are concerned about whether there was probable cause to search the van initially and whether a "chain of evidence" links the knapsack in the grass to the one Jewett saw Kabbani carrying.

Terwilliger said he would "not characterize" the manner in which the arrests were made. But he said, "I don't see any substantial legal impediment in terms of the progress of the case."Staff writer Mary Thornton contributed to this report.