UPDATE 2-Spain's Prisa Q1 net up, backed by advertising

(adds analysts)

By Elisabeth O'Leary

MADRID, April 17 (Reuters) - Spanish media firm Prisa (PRS.MC: Quote, Profile, Research) posted a 4.1 percent rise in first quarter net profit on Thursday in line with expectations and backed by strong advertising revenues, with TV compensating for weak ad income at older media units.

Analysts warned that the results were perhaps not as strong as at first appeared, with declining margins at key businesses such as flagship newspaper El Pais.

Many investors are on hold until the results of the company's buy-out bid for TV unit Sogecable SGCE.MC come out next month. Prisa holds a conference call on Monday at which more details are expected.

"Shares will probably not do much until we know how the takeover bid has gone, with many people expecting that their debt levels will rise to finance the bid," said Virginia Perez, analyst at Ahorro Corporacion Financiera.

First-quarter net profit came in at 25.2 million euros ($40.2 million) against an average forecast of 25.6 million euros in a Reuters survey of five analysts.

EBITDA (earnings before interest, taxes, depreciation and amortisation) rose 11.2 percent to 172.3 million euros, just ahead of expectations of 168 million euros.

Revenues rose 7.2 percent to 958.4 million euros against the survey average of 946.5 million euros.