Because of the security sweep, several hundred reporters and news crews spent up to two hours waiting to get to office space inside the zone.

''It's the Secret Service," said one Boston police officer, after he sent reporters to the wrong entrance. ''They keep changing orders."

About 500 journalists toting briefcases and cameras were herded around almost the entire perimeter of the FleetCenter, and across two ramps to Route 93 and onto the parking lot of the Spaulding Rehabilitation Center.

Another 200 journalists cooled their heels at one entrance to the FleetCenter for more than 90 minutes not knowing that the media at another entrance was finally gaining access, at least to the magnetometers.

''I've covered 10 conventions," said Mark Z. Barabak, a Washington correspondent for the Los Angeles Times. ''There's a lot of confusion. It doesn't seem like anyone knows what's going on."

The Secret Service chalked up the confusion to necessary precautions. ''The whole security screening process is a thought out and complicated process when we're doing something like this," said Ann Roman, a spokeswoman for the Secret Service.

Dump trucks from Boston Public Works blocked several streets leading to the security perimeter on Causeway Street, adding to the fortress-like atmosphere.

Two private security guards stood watch by a local Fox 25 news satellite truck parked on Friend Street outside the perimeter. The Fox 25 logo was covered with blue duct tape, perhaps in response to the FBI warning issued last week that a radical group of domestic terrorists may target news vehicles. Most network and local TV news trucks were parked in a designated lot inside the hard zone, authorities said.

A spokeswoman for CBS news said her bosses had instructed her not to talk about security preparations, but Sandy Genelius said, ''We feel we're as prepared as we can be."

Asked for updates about threats to media vehicles, Coast Guard Petty Officer Zack Zubricki said, ''There have been no incidents. It's been quiet so far."

The biggest sighting of the day by far was the arrival of a liquefied natural gas tanker traveling through Boston harbor with four tug boats flanked by four orange zodiac inflatable boats. Two US Coast Guard ships escorted the flotilla. Journalists standing on the roof of the nearby Boston Harbor Hotel gawked as the heavily fortified blue tanker cruised through the harbor with black military helicopters whirring overhead.

LNG tankers sailing into the Distrigas terminal in Everett have long been controversial as potential terrorist targets. Distrigas announced last spring that there would be no LNG tankers traveling into Boston during convention week. But Distrigas spokesman Douglas Bailey said yesterday that the delivery was planned well in advance with various law enforcement officials notified.

''We voluntarily scheduled our tankers' arrivals and departures so they wouldn't interfere with the DNC, which starts next week," said Bailey. ''We don't release when we bring them in," he said. ''Nobody is surprised by this."

Mayor Thomas M. Menino has repeatedly warned that LNG tankers pose a potential threat to the city when they cross the harbor and dock in Everett. But a spokesman for Menino, Seth Gitell, said that the LNG delivery yesterday was not a problem since the convention had not yet begun.

By last evening, there had been no security-related arrests.

But amid the heightened security, police answered an emergency call in Hyde Park yesterday and searched a privately owned school bus with Idaho plates that contained two small gasoline containers and a few 130-gallon propane tanks, Boston police said.

Some media members found amusement. Jim Mitchell, a CBS crew member, smiled at having to cross the highway to gain access to the magnetometers outside the media center. ''It was kind of insane," Mitchell said. ''Like, 'make way for the ducklings crossing Storrow Drive.' "

- Stephen Kurkjian and Glen Johnson of the Globe Staff and Globe Correspondent Jack Encarnacao contributed to this report.