POSTOJNA, Slovenia, April 12 (Reuters) - Four surveillance rooms believed to date back to communist-era Yugoslavia and filled with dust-covered listening equipment have been discovered behind a Slovenian hotel situated next to one of the world's largest limestone caves.

The wiretapping rooms were found behind a solid steel door during renovation work at the back of the Hotel Jama and lead directly to the Postojna Cave's interior.

The spy rooms were likely built around 1969 when the hotel was under construction, according to Marjan Batagelj who heads the company managing the hotel and cave, a major tourist attraction in the former Balkan state.

The absence of humidity in the rooms made them ideal locations to store sensitive equipment, Batagelj said, while the thick layers of dust suggest the rooms have laid undisturbed for years.

"Those centres were part of a wider wiretapping system operated by UDBA, the secret political police," said researcher Igor Omerza, who has published books on Slovenian history.

"They used this for surveillance of people they believed were their political opponents."

Omerza said Yugoslavia's former communist leader Josip Broz Tito used to stay at the hotel, as did foreign and local dignitaries. Cables running from the surveillance rooms to the hotel indicate some hotel rooms had also been tapped, he said.

"I don't think Tito himself was wiretapped, they probably wouldn't dare to do that, but anything is possible. I think they primarily wiretapped guests who met with him there, foreigners," he said.

Batagelj said he might open up the rooms to tourists.

Slovenia, an Alpine state of two million people, was part of communist Yugoslavia until 1991 when it declared independence, an event followed by a brief 10-day war.

Slovenia joined the European Union in 2004 and three years later became the first former communist state to adopt the euro. (Reporting by Gasper Lubej; writing by Marja Novak; editing by Richard Lough)