SAN JOSE, Costa Rica--Contra leaders met yesterday with peace mediator Miguel Cardinal Obando y Bravo and then announced that they will open direct cease-fire talks with Nicaragua's Sandinista government on Jan. 28.

Sandinista negotiators arrived in San Jose late Wednesday, led by Nicaraguan Deputy Foreign Minister Victor Hugo Tinoco. He said his team came to Costa Rica to begin immediate negotiations with the Contras, although the talks were set for next Thursday.

Contra leaders dismissed the unexpected arrival of the Sandinistas as a publicity stunt.

"The cardinal had no knowledge that the Sandinista commission would be here," said Adolfo Calero, a director of the rebel umbrella group known as the Nicaraguan Resistance at a news conference following a two-hour meeting with Obando y Bravo. "We do not know and the cardinal did not know how this confusion occurred."

The Sandinistas may want to hold the talks early in an effort to reach an agreement in time to head off approval of more U.S. aid for the Contras. The direct talks were not scheduled to open in San Jose until one day after President Reagan is expected to ask Congress for more Contra aid.

"[The Sandinistas] are simply playing games around a serious subject--the gaining of peace in Nicaragua," said Alfredo Cesar, another Resistance director.

The Contras have been fighting for six years to overthrow the Sandinista government.

Tinoco said earlier yesterday that the Sandinistas wanted to take advantage of the presence of both Obando y Bravo and the Contra leadership to get the cease-fire talks under way.

The talks next week will take place without Obando y Bravo, who said he has to be in Rome on Vatican business. The cardinal, Roman Catholic archbishop of Managua, said he designated top aides to mediate in his absence.

Obando y Bravo, himself a leading critic of the Sandinista government, was not available to answer reporters' questions after meeting the six Resistance directors.

"After trying for five months to have a meeting with Cardinal Obando, we had it today," Calero said "We agreed with him to have a face-to-face cease-fire meeting between the commission of the Sandinista government and the commission of the Nicaraguan Resistance on Jan. 28 in San Jose, Costa Rica."

He said the talks are expected to go on for two days.