MANAGUA, NICARAGUA, SEPT. 13 -- President Daniel Ortega revoked a law today that was used to confiscate the property of Nicaraguans living abroad and he pardoned 16 citizens of other Central American countries who are in prison here for rebel activity.

In measures Ortega said contribute to Nicaragua's compliance with a peace plan signed by the five Central American presidents, Ortega also announced that a dialogue between the government and the opposition political parties will begin Oct. 5.

Opposition leaders said they were disappointed with the announcement as they had been expecting Ortega to reopen the Roman Catholic Church's radio station, closed since January 1986.

Responding to the Reagan administration's announcement last week that it will seek $270 million in new aid for the Nicaraguan rebels, known as contras, Ortega warned President Reagan with an old Nicaraguan bird-hunting saying: "You're wasting gunpowder on vultures."

Ortega, addressing a crowd of Sandinista sympathizers in the town of San Jacinto, 25 miles north of the capital, said his troops are defeating the contras. He punctuated his point by displaying a CIA-supplied Redeye antiaircraft missile that he said was captured from contra fighters Saturday in the northern mountain region of Bocay and was the second seized this year.

"Not only the Soviet Union gives weapons to Nicaragua. The Nicaraguan people are also arming themselves with the weapons the United States gives to the mercenaries," taunted Ortega, referring to the contras.

Today's measures came in a series of government gestures to show it intends to carry out the peace accord signed Aug. 7 in Guatemala. The plan calls for democratic freedoms to be established and for an end to guerrilla warfare throughout the region. The main clauses do not take effect, however, until Nov. 7.

The 1981 law that Ortega struck down empowered the government to confiscate the property of any citizen who remained outside of Nicaragua for more than six months. It was used to punish hundreds of exiled well-to-do opponents of the Sandinistas. Some fled political persecution, while many middle-class professionals sought to make a better living abroad as the Nicaraguan economy faltered in recent years.

Ortega said he canceled the law to encourage Nicaraguans to come back to live in their country.

But Enrique Sotelo Borgen, a leading opposition lawyer and National Assembly deputy, said the law had not been used in recent years. Calling Ortega's action a "mockery" of the peace plan, Sotelo noted that the Sandinista president did not promise any former owners they would get their property back.

Ortega clarified that no properties seized from associates of the late dictator Anastasio Somoza or expropriated under the sweeping Sandinista agrarian reform would be returned.

As for the pardon, Ortega noted that the 16 Central Americans were jailed for collaborating with the contras. The number of Nicaraguan prisoners linked to political opposition is estimated at more than 5,000.

Last month, Ortega named the government's most powerful critic, Roman Catholic Cardinal Miguel Obando y Bravo, to head a four-man commission to lead the political dialogue and verify compliance with the pact. Two priests who had been expelled, Nicaraguan Msgr. Bismarck Carballo and an Italian missionary, the Rev. Benito Pititto, were allowed to return yesterday. Carballo was director of the Catholic Radio when he was barred in June 1986.