A wire service table of major earthquakes in yesterday's editions failed to list the 1964 Alaska earthquake that measured 8.5 on the Richter scale and killed 114 people.

A devastating earthquake off Mexico's Pacific Coast struck the world's most populous urban area yesterday, toppling scores of buildings in Mexico City, causing serious damage in at least four states and leaving hundreds dead or injured.

The quake, measuring 7.8 on the Richter scale, severed all telephone and telex communication with Mexico City and reportedly left hundreds of persons trapped in the debris of collapsed hotels and apartment buildings.

The earthquake struck just before Mexico City's morning rush hour, at 7:18 a.m. (9:18 a.m. EDT), and lasted 4 1/2 minutes. Damage was reported in the states of Jalisco, Michoacan, Colima and Guerrero.

The armed forces estimated that 400 persons were killed in the capital. Mexico City has a population of more than 17 million, and it was feared that the death toll would rise past 1,000.

Mexico City Mayor Ramon Aguirre said at a news conference late yesterday that he "wouldn't dare" estimate the number of dead.

President Miguel de la Madrid appealed for calm in a radio broadcast, and the Defense Ministry put the nation's disaster-relief plan into effect, the State Department said in Washington after contacting the U.S. Embassy in Mexico City by radio.

De la Madrid toured some of the hardest hit areas. At one hospital, he told a reporter, "At this moment, our priority is to rescue victims and help them."

Troops were called out to prevent looting as firefighters battled blazes across Mexico City. Initial reports said that between 35 and 50 percent of the older buildings had suffered damage in Mexico City. Little information was available about other areas of the country.

The U.S. Embassy in Mexico City reported extensive gas leaks, a State Department spokesman said. Other reports said the subway system and electricity to about half the city had been cut off.

A Mexican television broadcast monitored in Guatemala showed firefighters battling to put out blazes started by the quake and children being treated for injuries outside a school whose three-foot concrete columns had snapped, news agencies reported.

The Spanish International Network, received via Channel 14 in the Washington area, showed live views of the damage and Mexican broadcasts via satellite. Mexico's Channel 13 called the damage "incalculable" and said that authorities had asked people to refrain from using gas or electricity for fear of touching off explosions and new fires.

Television broadcasters in Mexico City urged residents to leave damaged buildings to avoid more casualties. The broadcasts said several government buildings, including the Navy and Labor departments had been damaged.

The Mexican newspaper Excelsior notified journalists meeting in Havana that the death toll stood at about 3,000, Agence France-Presse reported, and Mexico City's Channel 2, monitored in Honduras, said there were 700 dead, but these reports could not be confirmed.

The old part of the city was reported to be the hardest hit. The Mexican broadcast showed scenes of widespread devastation, including caved-in buildings with columns of smoke rising from them and smashed automobiles tossed "like children's toys."

Paul Conklin, a Washington photographer who was in bed in his room on the seventh floor of Mexico City's Ambassador Hotel when the earthquake struck yesterday morning, described the scene as "total chaos."

He said the room started shaking and then "it was as black as night. An enormous cloud of dust must have come up and enveloped the city."

"Our hotel was demolished," he said, describing "enormous cracks in the outer wall. . . . No one will ever use that place again."

"The principal destruction was all downtown," Conklin said. "I would be very surprised if there were any buildings downtown that weren't structurally damaged."

Conklin said he shot a roll of film before taking a cab to the airport and catching what he believes was the last plane out.

"I was really in a state of shock," he said.

The U.S. Embassy reported "no known injuries" to U.S. personnel nor to U.S. citizens in Mexico, the State Department said. Mexico City's airport was closed for several hours.

Western Airlines said that it had received clearance for a flight originating in Los Angeles to land in Mexico City, provided that it refueled elsewhere. A Western spokesman said the jet fuel supply at the airport had been contaminated.

The earthquake's epicenter was placed at 250 miles southwest of Mexico City by the U.S. Geological Survey in Golden, Colo., and tremors were felt as far away as Houston. The most recent severe earthquake in Latin America was March 3, when one measuring 7.4 on the Richter scale left at least 177 persons dead in Chile.

M. Peter McPherson, administrator of the Agency for International Development, said last night that the U.S. government stands ready to assist Mexico.

"We are greatly concerned about the extent of injury to people and damage to property in Mexico," McPherson said. "We are prepared to offer immediate and appropriate assistance as requested."

The Mexican Embassy in Washington said it had no means of communicating with the Mexican capital. "Unfortunately, there is no possiblity of contact," an embasssy spokeswoman said.

Government-owned Channel 13 at one point was the only working television station in Mexico City. The Associated Press, monitoring the radio, reported scenes of hospitals filled to capacity with injured people, and told of devasted buildings and flattened buses and cars.

Twenty-five persons were killed when a church collapsed during mass in Ciudad Guzman, 275 miles west of Mexico City, United Press International reported, quoting El Informador newspaper in Guadalajara. The paper also reported "extensive damage" in the nearby city of Colima.

Radio stations broadcast urgent appeals for motorcycle owners to lend their vehicles to emergency rescue personnel to help get them through the traffic, news agencies reported. There were also appeals for blood and for heavy earth-moving equipment to aid in the rescue efforts.

An AT&T spokesman in New Jersey said it is not possible to call the 905 area code, which covers Mexico City, but other parts of Mexico can be reached by phone. The spokesman said the company had offered the Mexican telephone company, Telefonos de Mexico, assistance in the form of emergency microwave towers, power generators and other equipment.

Much of what information was available from Mexico came through amateur radio operators.

"Rescue work in the buildings is becoming more difficult now. It's getting dark, and all electrical service in Mexico city is out," said a ham radio operator monitored by Walter Wurfel of Arlington. The ham operator, broadcasting in unaccented English from a location near Mexico City, said, "This is a real emergency down here."

Radio Colombia in San Jose, Costa Rica, also monitored by Wurfel, said that 300 buildings in the center of Mexico City were destroyed.

"There is much damage in the state of Jalisco," the Costa Rican radio station said, adding, "The number of dead is minimal in comparison with what it would have been if the quake had occurred at 8 or 8:30, when children were on their way to school."

Five radio journalists died at a Mexico City radio station when the station's transmitting tower fell on the roof and the roof collapsed, Radio Colombia reported.