Liberia said yesterday that 10 prominent opposition politicians, a businessman and a journalist were in "protective custody" and suggested that many of them would be tried for complicity in last Tuesday's attempted coup.

A spokesman for the Liberian Embassy here also repeated denials of reports that several of the opposition leaders had been executed by the government of Maj. Gen. Samuel K. Doe.

A State Department spokesman said yesterday that the United States has conveyed to Liberia "the importance we attach to its ensuring that due process is granted to all those who have been taken into custody. We have not yet received a satisfactory reply."

There have been persistent, but unconfirmed, reports that several opposition leaders had been executed summarily, including Liberia Action Party presidential candidate Jackson F. Doe, no relation to Samuel Doe, and another leading party figure, former finance minister Ellen Johnson-Sirleaf.

Gen. Doe accused Johnson-Sirleaf of financing the coup attempt, which came less than a month after a disputed presidential election. Samuel Doe was declared the winner of the Oct. 15 balloting, but informed observers who monitored the vote said Jackson Doe appeared to have won a clear majority. Three opposition parties, including the Liberia Action Party, rejected the announced outcome.

J. Emmanuel Bowier, the embassy's counselor for public affairs, said religious leaders and members of the diplomatic corps were summoned to a briefing by Doe on Friday at which an alleged member of the group that tried to seize power revealed details of the coup attempt, including alleged participation by mercenaries from Sierra Leone, Cuba and Guinea.

Bowier also said Jackson Doe and two other opposition leaders were at the briefing, but this could not be confirmed independently.

Besides Jackson Doe and Johnson-Sirleaf, Bowier said those in custody are Byron Tarr, David Farhat and Emmanuel Koromah, all of the Liberia Action Party; Carlos Smith, S. Jackson Carlon and presidential candidate Edward Kessely of the Unity Party; Gabriel Kpolleh, another presidential candidate, and Leslie Green of the Liberia Unification Party; businessman Emmanuel Shaw and Momolu V. Sirleaf, managing editor of the Footprints newspaper.