MADRID Tenor Plácido Domingo, 72, was admitted to hospital on Monday for treatment of a pulmonary embolism , or blood clot on the lungs, according to management at the Teatro Real yesterday. Domingo is being treated 'successfully' but will have to take 3 or 4 weeks' rest for a full recovery. This will preclude him from performing in the opera Il Postino, by Daniel Catán, in which Plácido Domingo takes the part of renown Chilean poet Pablo Neruda. He had planned to call a press conference to announce his return to the Teatro Real with this opera, in which he had performed before at other venues. He will not be able to take part, either, in a free concert on Sunday 21 at which he was to direct the Comunidad Valenciana Orchestra.