A senior U.S. State Department official who met twice with Gen. Manuel Antonio Noriega last week secretly flew to Panama for more talks amid reports the Reagan administration may soften demands for Noriega's departure, sources said.

The reported Wednesday arrival of Michael Kozak, a deputy to Assistant Secretary of State Elliott Abrams, came as police raided the offices of opposition activists on the eve of a planned demonstration Thursday by the anti-government Civic Crusade.Prosecutors said they had uncovered a "plot to subvert public order" and ordered the arrests of an unspecified number of opposition organizers.

Kozak met with Noriega April 18-19, reportedly to tell him the United States was willing to consider a more flexible approach in its 2-month-old effort to oust him from power.

Sources in Panama who knew of Kozak's last secret trip told United Press International he was scheduled to meet with Noriega Wednesday. State Department spokesman Charles Redman would not comment on the reports, saying, "I would put that in the category of not getting involved in what our particular diplomatic initiatives are, where they may stand."

U.S. officials are frustrated with the failure of current efforts including economic sanctions and refusing to recognize his government to unseat Noriega.

President Eric Arturo Delvalle ordered Noreiga to step down to face drug charges in the United States Feb. 25 and instead was ousted by the pro-Noriega National Assembly. Delvalle has been in hiding and was replaced by Manuel Solis Palma.

In the past, the Reagan administration has demanded that Noriega step down immediately and go into exile, but those demands are now widely recognized as unrealistic.

Sources say the United States now would be willing to approve a solution that would allow Noriega to step down with full honors and without admitting he caved in to U.S. pressure.

One source said such a scenario would require that Noriega publicly commit himself to leaving by a specific date, after which the Reagan administration would ease the economic pressure that has severely damaged Panamanian finances.

Other sources said Noriega is demanding that Washington drop federal drug trafficking charges filed against him in Florida, or that they be forgotten if he goes into exile.