Leftist guerrillas seized Dominican Republic's embassy during a reception today, taking the U.S. ambassador and a large portion of Bogota's diplomatic corps hostage.

A Colombian guard was reported killed in the violent takeover, and among several persons wounded was the bodyguard of U.S. Ambassador Diego Asencio.

The Colombian government announced tonight that it has named former foreign minister Alfredo Vasquez Carrizosa to mediate the crisis and that he entered the Dominican Embassy residence to begin negotiations with the guerrillas holding the diplomats captive.

With Vasquez was Ernesto Martinez, who has been approved by the guerrillas, a government statement said.

Other ambassadors reportedly held with Asencio by the heavily armed assailants include those of Uruguay, Austria, Switzerland, El Salvador, Costa Rica, Brazil, Guatemala, Egypt, Venezuela, Mixico, Haiti, Israel and the Dominican host as well as the papal nuncio and a U.N representative. The reception was in honor of the Dominican independence day.

Colombia and neighboring Venezuela are the only major countries in South America maintaining a tradition of democratic rule. Colombia has battled both leftist guerrillas and drug traffickers with increasing intensity, triggering charges of human rights violations.

The guerrillas at the embassy, in phone interviews, demanded release of more than 200 leftists they said are now in jail, $50 million ranson and withdrawal of the police surrounding the embassy. Otherwise, they said, the embassy would be blown up.

[A State Department spokesman said the U.S. government, in close contact with the government in Bogota, "was assured that Colombia will not take precipitous action." Ambassador Asencio had been allowed to talk with the authorities by phone and said he was "well and calm," according to a U.S. official.]

[Secretary of State Cyrus Vance said, "This despicable and dishonorable act is another example of terrorist violence against accredited foreign personnel. It cannot be excused or tolerated."]

A Colombian radio chain initially reported, erroneously, that Asencio, 48, was outside during the attack and wounded. His Colombian bodyguard, hit while waiting by the envoy's car, was taken to a hospital, according to the U.S. Embassy.

Mexico's ambassador shouted from a window to reporters that a Paraguayan diplomat had been seriously wounded and that four other wounded persons were among the 44 hostages inside.

Asencio, who is a Spanish-born naturalized American, is a Georgetown University graduate who has served here since 1977. He has been outspoken on the danger posed to Colombia by the billions of dollars in drug-trafficking generated by the American market. He has also praised Colombian efforts to curtail it.

At the embassy in west Bogota, a city of 3 million persons, diplomats shouted from the windows that if police approached, the guerrillas would set off explosives. One of the guerrillas yelled that the group was a "combined command" of M-19 -- Colombia's most notorious guerrilla group -- and he demanded that President Julio Cesar Turbay enter negotiations of release of the hostages.

A communique issued by the Colombian Defense and Communications Ministries also said the M-19 group was apparently responsible.

The M-19, a Marxist group whose formal name is the April 19 Movement, was thought to have been virtually destroyed when a drive by military police last year resulted in the arrest of some 200 of its purported leaders.

Taking its name from the date of a presidential election in 1970 that the group said fraudulently prevented the election of populist Gustavo Rojas Pinilla, the group has gone in for spectacular acts.

It stole the sword of liberator Simon Bolivar and in January 1979 tunnelled into a military arsenal and carried off 4,500 weapons. Other lefists have accused M-19 of having more interest in publicity than revolution.

Witnesses said the gunmen barged into the embassy today with guns blazing.

"The young men were wearing orange and blue sweatshirts and were walking past the embassy when a Mercedes Benz with an ambassador arrived," a witness told the radio station Caracol. "It was then that the young men penetrated the embassy. Then the bodyguards of the ambassador who arrived open fire, too, and there were several people wounded, including one of the attackers who was shot in an arm," the witness told reporters at the scene.

Gunfire broke out twice in the vicinity of the embassy after about 500 policemen surrounded the building, across the street from the National University.

Students harassed security forces by chanting slogans favorable to the leftist occupiers and crowds of curious onlookers surrounded the area where police barricades sealed the zone in a seven-block radius. The University campus has been guarded by troops since the government suspended classes earlier this month to prevent leftist demonstrations.

In addition to the ambassadors held hostage, according to the government's communique, the charges d'Affaires of Paraguay and Bolivia and numerous Colombian Foreign Ministry officials were inside.

Argentina's ambassador was reported to have arrived late and to have managed to retreat safely when the assault began.

One of the guerrillas called for police to send an ambulance to pick up Venezuelan Ambassador Virgilio Lovera, saying he has suffered a heart attack.

Colombia, with a population of 25 million, is the most populous country in South America after Brazil. It has maintained a highly specialized form of democracy since a compact ended a bloddy civil war, fought between followers of the traditional Conservative and Liberal parties, 25 years ago.

More than 100,000 died in that fighting and the elected governments since then -- which until recently were required to alternate between Conservative and Liberal rule -- have been quick to use the often ruthless police in any civil unrest.