WASHINGTON – The United States announced new measures to combat sky terrorism Monday as relatives of passengers killed in the Pan Am Flight 103 bombing mounted a campaign to complain about aviation security and the government’s “lack of compassion” following the disaster.

Transportation Secretary Samuel Skinner, who along with President Bush met with several relatives of those killed in the explosion over Scotland, told a news conference that airlines will be required to install devices to detect plastic explosives in major U.S. and foreign airports.

Relatives of victims in the Dec. 21 explosion, which has been blamed on a plastic device hidden in a radio-cassette player, praised Bush for concern shown in the meeting and said Skinner’s announcement was a good first step.

But spokesman Bert Ammerman of Demarest, N.J., told a rally across the street from the White House that measures announced by Skinner were “not enough.”

Ammerman, whose brother Tom was one of 270 victims of the crash, asked for a unified congressional investigation of the disaster, hand-searching all luggage put aboard airliners, and an end to a system that allows notification only of airline, airport and government security personnel when there is a terrorist threat.

Skinner said he would recommed against a coordinated congressional inquiry, although Bush told the relatives he would consider pressing for such a probe as opposed to several separate congressional investigations.

Skinner said the FBI and Scotland Yard were best qualified to conduct the criminal investigation, and there is no indication government response to the explosion has been inadequate.

The transportation secretary, in his announcement, also ordered airlines to acknowledge all Federal Aviation Administration security bulletins within 24 hours. He said compliance would be mandatory.