OKLAHOMA CITY A thundering, half-ton car bomb blew away nearly half of a nine-story federal building Wednesday in Oklahoma City, killing 31 people, including 12 children, leaving 300 people missing and stabbing an icy fear of terror into the American heartland. Authorities said they were certain that the death toll would climb. For hours, many of the dead were impossible to reach in the tangled wreckage.


The blast sent a red-orange fireball into the blue sky and rocked the flatlands for 30 miles around. It threw a dirty black cloud of smoke and debris high into the air and hurled shards of glass in every direction around a ragged five-block circle. Cars in the streets nearby burst into flames and exploded. Men and women screamed and ran for their lives.


Rescuers brought most of the injured including children as young as 18 months old who were bloody and battered to St. Anthony Hospital, which reported treating more than 200 people for cuts, burns and shattered bones. A nurse, bloodstained and crying, said: ``I was shocked to think that someone could do that to small children.''


All of America was shocked. Here are some of the day's developments:


President Clinton called the bombers ``evil cowards'' and asked people to pray for the victims.


Vowing that the world's best investigators would pursue the guilty, Clinton said, ``These people are killers and must be treated like killers.'' When they are found, ``justice will be swift, certain and severe,'' the President promised.


``I was sick all day long,'' he said in an interview with KCCI-TV of Des Moines, Iowa. ``All of us have been looking at the scene where those children were taken out, and all of us were seeing our own children there. This is an awful, awful thing.''


U.S. Attorney General Janet Reno vowed to punish those responsible with death. Oklahoma Gov. Frank Keating said that if terrorists can strike in the safe and placid heart of America, then it is ``an awful statement about the evil that lurks in the world.''


Even before the smoke cleared, federal investigators began a search for tell-tale signs of ammonium nitrate and kerosene, critical ingredients in the explosive that damaged the World Trade Center in New York City more than a year ago.


Dick Deguerin, an attorney representing the Branch Davidian religious sect, denied any involvement and said that all remaining members were at a memorial service for those killed in a standoff with federal agents two years ago to the day in Waco, Texas. And American Muslims asked the media to exercise restraint in reporting unsubstantiated accusations against them.


While hundreds of leads were being investigated, a number of law enforcement sources and private terrorism experts said that the bomb apparently used bore the basic characteristics of devices that Muslim extremists have detonated in such places as Beirut, Lebanon and Buenos Aires.


One source familiar with the investigation said that the FBI had received claims of responsibility from at least eight groups seven of which seemed to be of Middle Eastern origin. Authorities were uncertain how credible the claims were, but were taking all leads seriously, the source said.


The FBI has been aware of the activity of Islamic student groups meeting recently in Oklahoma City, Dallas and Kansas City. Federal authorities have long feared that the groups may have ties to radical elements, including the militant Middle Eastern group Hamas. Leaders of Hamas and another militant group, Islamic Jihad, were among the speakers at an Islamic conference held in the Oklahoma Convention Center in 1992.


Officials in Washington discounted the importance of an Oklahoma television station report that authorities had ordered a search for two individuals with a ``Middle Eastern'' appearance, traveling in a brown Chevrolet pickup truck. That could have been just one of hundreds of tips that would have been automatically pursued, the officials said.


The Dallas Morning News reported that a National Car Rental spokesman said the FBI suspected that a vehicle involved in the attack was rented at the company's Dallas/Fort Worth office. Oklahoma City television reported that the Oklahoma City police department had found a piece of a maroon minivan that may have been used to carry the explosives.


Fragments of the exploded vehicle's license plate also were found, television reports said, and indicated that the minivan had been leased from a National Car Rental agency. But in Washington, federal investigators said they knew nothing to confirm these reports.


The terror began shortly after 9 a.m.


Hundreds of employees had reported for work at the Alfred P. Murrah Federal Building, which houses offices of agencies such as the Bureau of Alcohol, Tobacco and Firearms, Social Security, Veterans Affairs, the Drug Enforcement Administration, Housing and Urban Development, a federal employees credit union and military recruiting offices.


Many had dropped off their children at a day care center on the second floor. Employees in other downtown offices had just brought their youngsters to another day care nursery at the YMCA nearby.


With a rumble, a bomb thought by some authorities to have been in a parked vehicle near the front of the building exploded and sent the entire north side of the structure crumbling to the ground.


The bomb was large, perhaps 1,000 to 1,200 pounds, said John Magaw, director of the ATF. Keating told reporters: ``Obviously no amateur did this. Whoever did this was an animal.''


Workers, some in their underwear because the blast had torn their clothing off, staggered, screaming, out of the building. They were covered with glass, plaster and blood. Many were in tears.


Rescuers began wading into the rubble with chain saws. Periodically they turned them off to listen for moaning, calls for help or other sounds of life. Most often, all they could hear was silence.


At one point, sheriff's deputies told more than 75 doctors and nurses at a triage area nearby that anyone who was still inside had to be dead.


Sixty firefighters worked in teams. ``We've got to believe we've got some survivors,'' said Assistant Fire Chief John Hansen. ``That's what's keeping the rescue workers going.


``We gotta hope for something.''


The rescue teams struggled from floor to floor. By afternoon, they had made it to all of the floors, but had been able to make a thorough search of only about one-third of them. Much of the building was impassible.


As evening approached, the teams counted 58 successful rescues.


As darkness fell, it grew harder and harder to find anyone still living. Nine dogs trained to pick up human scent spent four hours going through the wreckage.


Karen Hardesty, a representative of Oklahoma Canine Search and Rescue a non-profit volunteer group that brought the dogs from Tulsa said they sniffed out 40 to 50 people, but none of them was alive.


Rescuers brought in large lights so they could continue searching into the night. But growing rain presented a particular problem. Water would weigh down weaker parts of the building and add to the threat of collapse.


``As much as we like to rescue any survivors,'' said Hansen, the assistant fire chief, ``We've got to slow down and be very, very cautious.''


He said his men would have to crawl over corpses to get to anyone alive.


The horror of the day was recounted later by physician Gary Massad, who, with two other doctors, amputated the right leg of a 20-year-old woman just below the knee to free her from beneath a large concrete block in the basement. Massad said it took more than an hour to reach the woman because of the mass of debris and the unsteady interior of the building. The 20-minute amputation was performed without a general anesthetic by surgeon Andy Sullivan as he lay on his stomach across the woman's body in about a foot of water that had collected in the basement, Massad said. He said the last time he saw the woman, when she was freed at 3 p.m., she was alive.