Michael Ruddy bowed yesterday to the threat of terrorism inspired by hostility in the Persian Gulf and canceled a field trip for his high school students from Bloomfield, Mich., to Europe and the Soviet Union.

Tony Quay, a physician in Santa Fe, N.M., has examined patients recently with tension headaches and muscle spasms that they guessed might be caused by the angst of having relatives waiting in the Saudi Arabian sands.

Keeley Lekavich, an American Red Cross employee in Raleigh, N.C., said yesterday that she feels "a sort of a depressing kind of wait" in her office as the nation slides inexorably into the final hours of the U.N. Security Council deadline for Iraqi President Saddam Hussein to withdraw his forces from Kuwait.

While Pentagon insiders may debate whether the shot that begins the Persian Gulf war will be fired at midnight tonight, the moment has become a psychological deadline for thousands of military families separated by the U.S. troop deployment in the gulf and for a nation deeply confused and saddened about what appears to be the inevitability of unthinkable destruction.

In dozens of interviews nationwide yesterday, those who support the use of force against Saddam and those who prefer to give economic sanctions more time expressed anxiety and depression about what most said would be a violent course of events.

"I think it's clearly not just another day," said Ruddy, a teacher at the private Roeper City and Country School. "This is the first day in my lifetime when we'll have a scheduled war. I get a sense of foreboding, especially because I don't know if there was a right course of action."

Some people, such as Nancy Rader in Cando, N.D., whose husband is in Saudi Arabia with the National Guard, will stay quietly at home. She will be with her mother-in-law and the newborn girl whom her husband, Gary, has never met. "The speculation up to this point has caused too much anxiety," she said. "It's absolutely nothing we have control over. We feel so helpless. As a self-defense mechanism, we will try to push it back and not talk about it."

For others, this is a time for collective action and group support.

Police arrested 127 of an estimated 3,000 anti-war protesters who marched through the downtown Chicago yesterday during morning rush hour shouting, "No blood for oil." In Minneapolis, demonstrators blocked entrances to the old Federal Building and burned an American flag. In California, several hundred marchers stalled traffic on the Golden Gate Bridge while 1,500 protesters walked through downtown Santa Cruz. In Seattle, congregants at the University Baptist Church voted to give sanctuary to war resisters, while police stormed demonstrators at a Detroit military recruiting station, arresting at least 14 people.

Security at airports was reportedly tightened yesterday to respond to worries about terrorist retaliation for U.S. military action. A crudely made firebomb was tossed through the glass door of an Army National Guard recruiting station in Puyallup, Wash. The bomb did little damage and police said the motive was not known, although investigators speculated that it could be related to gulf tensions, the Associated Press reported.

Even in some churches, gloom has overtaken the solace of the sanctuary. "There's a sense that things are spinning out of control, that this could be a time of divine retribution," said the Rev. David Wilkerson, pastor of the 3,000-member Times Square Church in New York City, an interdenominational, evangelical Protestant church. "In our church, there's a kind of apocalyptic sense that the world is on the verge of spiritual reviving, and yet of destruction."

Like nearly every community in the nation, Miamians attended prayer and peace vigils over the weekend. "I haven't been this frightened since the Cuban missile crisis," said Cherry Krech, who organized one prayer vigil. The mayor's office reported calls from constituents wanting to know the location of bomb shelters.

At Mount Calvary Baptist Church in the city, Lebbie Lee attended a peace vigil Friday afternoon, and broke down in tears as the congregation began singing and clapping. Her son, an Army soldier in Saudi Arabia, had recently phoned home with the news that he'd been inoculated against chemical weapons. "He's on the front line," Lee said. "I'm praying very hard."

It is around the near-empty military bases that the pain over the possible consequences of war are the most vivid.

At Fort Hood, Texas, the nation's largest military base, 20-year-old Clint Lee stood outside the massive commissary and thought about his older brother stationed in Saudi Arabia.

"I'm scared now," he said. "I figured this thing would have ended a long time ago. I'm still hoping something good would happen, but I feel sick about it now."

The sounds of war were literal and constant: artillery shells exploded on the test ranges at all hours of the night and day, shaking the barracks inside the fort and rattling windows in nearby housing tracts.

To Andrea Dally, whose husband, Sgt. Thomas Dally of Alpha 92 of the 2nd Armored Division, has been in Saudi Arabia since October, the cracks and booms were somehow reassuring. "I find it comforting to hear those noises -- they are a part of life here," she said. "It's when they stop that this place seems like a ghost town and the silence is deadly. That's when I get scared thinking about what might happen."

For people like Patti Williams, a 26-year-old hairdresser at a West Los Angeles mall, the deadline will pass without much notice. "To tell you the truth, I haven't been following it much. I don't let it interfere with my life."

For others, the day will be a timeless one. "Forty-one years ago yesterday I was in the snows of Luxembourg with some shrapnel in me," said George Cook, co-owner of Elverson Supply Co. in Elverson, Pa. who is opposed to going to war with Iraq. "It's more on my mind today because you keep thinking somebody's going to blink, but nobody's blinking. . . . There's just no good answer."

Contributing to this report were staff writers David Maraniss in Killeen, Tex.; Jay Mathews in Los Angeles and Laura Parker in Miami, and special correspondents Christopher B. Daly in Boston, Laurie Goodstein in New York and Lauren Ina in Chicago.