A warning from an overseas informant that terrorists planned to detonate explosives in a tunnel under the Baltimore harbor led state officials to temporarily close one of the harbor's two highway tunnels shortly before noon yesterday and to restrict travel in the other tunnel, officials said.

Less than two weeks after the New York subway system was blanketed with security because of a terror threat that proved unsubstantiated, the Harbor Tunnel on Interstate 895 was closed for more than 90 minutes and vehicles were searched at the Fort McHenry Tunnel on I-95, where one lane remained open in each direction. Anti-terror investigators conducted interviews and searches in response to the informant's tip, which federal officials said was uncorroborated.

Three Egyptians and one Jordanian -- all connected to businesses in the Baltimore area -- were detained on immigration violations as a result of the interviews, a federal law enforcement source said. The source spoke on the condition of anonymity, as did others for this article, because of the sensitivity of the investigation.

"The information was somewhat specific as to date and time," said Kevin Perkins, special agent in charge of the FBI's Baltimore field office. "At this point, no evidence collected to date has corroborated the threat."

Perkins did not describe the tip in detail. According to two law enforcement sources, authorities were acting on information that six Egyptian or foreign terrorists were to receive bomb-making materials by ship, assemble them and load them onto vehicles to be detonated in one or both tunnels.

Yet even as investigators continued to pursue the possibility that terrorists had targeted a tunnel, others questioned the effectiveness of the government response. Some drew parallels to the transit-system warning issued in New York by Mayor Michael R. Bloomberg (R) in response to information, also from an overseas informant, that authorities in Washington described at the time as "non-credible."

Rep. Jane Harman (Calif.), ranking Democrat on the House intelligence committee, said the episodes show that the homeland security intelligence system "is seriously challenged" and not coordinating as it should.

"Data collection may have been flawed. The analysis may have been flawed. Adequate information may not have been shared, and we still have turf wars going on," Harman said. "It surely doesn't make local officials happy."

Mayor Martin O'Malley (D) and Baltimore Police Commissioner Leonard D. Hamm said they learned of the tunnel closure from the news media -- an apparent communication failure that O'Malley termed a "little glitch."

"I'm not aware of what the grounds were to close it," said O'Malley, speaking at police headquarters. "Maybe there are facts. I'm not aware of those facts if they exist."

Gary W. McLhinney, chief of the Maryland Transportation Authority Police, defended his agency's decision to close the tunnel. "I'm not going to hesitate to close a facility if I think it's the proper thing to do," he said. "We're going to err on the side of public safety each and every time."

Appearing later with FBI and state officials at an afternoon news conference, Gov. Robert L. Ehrlich Jr. (R) called the day's operations "seamless." Ehrlich downplayed O'Malley's concerns, as did McLhinney, who said city police officers were included on a task force that was working on the case and that had been briefed on potential tunnel closures.

Ehrlich appeared annoyed by continuing media questions about what city officials knew, breaking in at one point to note that there was no phone call made right beforehand to Baltimore County Executive James T. Smith Jr., whose jurisdiction also was affected.

In a joint statement, the FBI and the Department of Homeland Security described the warning as a "potential threat of undetermined credibility to an unspecified tunnel." The agencies said, "We support whatever protective measures" state and local officials deem necessary until the investigation is completed.

"At this time, we're taking it seriously and, later on, based on the information we get, others can make the determination of whether it's credible or not," said James M. Pettit, a spokesman for the governor's office of homeland security. "We're just acting out of an abundance of caution."

According to a law enforcement source, the overseas informant provided the names of several people said to be involved in, or to have knowledge of, the alleged threat.

"We're taking it seriously because the person is naming names," the source said. "It might not turn out to be anything."

Staff writers Spencer S. Hsu, Sari Horwitz and Mary Otto contributed to this report.

A Maryland Transportation Authority Police officer talks with a tractor-trailer driver near the southbound entrance to the Fort McHenry Tunnel.Diverted traffic is lined up at the Francis Scott Key Bridge in Baltimore after the closing of the Harbor Tunnel because of a warning about terrorism.