The White House announced this afternoon that 12 jailed members of a Puerto Rican nationalist group had accepted President Clinton's conditional offer of clemency. Eleven will be eligible for release within days, while the 12th had his 55-year sentence drastically reduced and will be paroled in five years.

Two other jailed members of the radical group, known as F.A.L.N., the Spanish initials for the Armed Forces of National Liberation, refused to accept the President's offer to commute their sentences. Mr. Clinton demanded as one of the conditions of their release that the jailed Puerto Ricans renounce the use of terrorism to achieve their aim of independence for the Caribbean commonwealth.

Roberto Maldonado-Rivera and Norman Ramirez-Talavera, who both were released from prison several years ago after serving their sentences in a 1983 armored car robbery in West Hartford, Conn., have not replied to the clemency offer and have until Friday to do so. The clemency offer would forgive the unpaid balance on fines imposed on them in the case.

Joe Lockhart, the White House press secretary, said in a written statement this afternoon: ''The President expects all those who accept the conditional clemency grant to abide fully by its terms, including refraining from the use or advocacy of the use of violence for any purpose and obeying all the statutory conditions of parole.''