Government troops claimed to have regained control of the north central city of Jinotega this morning following three days of heavy fighting there with Sandinista Liberation Front Guerrillas.

Entry to the area remained prohibited, however, and scattered gunfire could be heard beyond a National Guard roadblock established outside the city. Nevertheless, a Guard communique said that the city was "under government control."

Earlier this week, the guerrillas claimed to have "liberated" both the town and a large mountainous zone north of it. Fighting, including heavy aerial bombing, is said to be concentrated now in small viallages and rural areas.

Meanwhile, the governments of Colombia, Panama and Venezuela have indicated they do not intend to break relations with Nicaragua, despite a joint appeal from Costa Rica and Mexico. In turning the appeal down, those countries said they wanted to keep their embassies here open for the hundreds of Nicaraguans who have taken asylum inside them. They also said they could better affect the situation by maintaining ties despite their open opposition to the government of President Anastasio Somoza.

Costa Rica broke relations with Nicaragua last fall. On Monday, President Jose Lopez Portillo, citing "horrendous genocide" by the Somoza government, severed Mexico's diplomatic ties.

The Mexican Embassy, in which more than 30 Nicaraguans remain in asylum, is now flying the Peruvian flag. The four Mexican diplomats still here referred all questions to the embassy of Peru, which they said, is handling Mexican affairs.

Although sources close to guerrilla leaders have said that this week marks the beginning of an allout Sandinista offensive, events so far appear more to be a continuing escalation of Nicaragua's nine-month civil war.

On Monday night, the homes of four government officials, including National Guard inspector general Jose Somoza, the president's half-brother, and interior minister Antonio Moro, were attacked with gunfire and rockets. No serious injuries were reported, but the attacks brought forth a pledge from a clandestine, rightist paramilitary organization to exact revenge.

Last week, a number of opposition leaders and journalists received anonymous telephone threats. At least 40 persons were said to be marked for assassination should a guerrilla offensive begin.

Yesterday, telephone callers to La Prensa, the opposition newspaper, said that the Monday night attacks were being taken as a signal of that offensive and retaliation would now start.

Some of the people listed for killing have lfet the country or are in hiding, and as yest no action linked to the the purported rightist group has occurred.