ROME, Jan 23 (Reuters) - Budget airline Ryanair would be interested in acquiring Italian airport slots that might be relinquished as ITA Airways joins forces with Lufthansa , Ryanair CEO Michael O'Leary said on Tuesday.

Speaking at a news conference in Rome, O'Leary said that Ryanair, which is the biggest airline operator in Italy, believed that slots should be released at Rome's Fiumicino airport and the Malpensa and Linate airports in Milan.

Lufthansa is seeking to acquire a 41% stake in ITA for 325 million euros ($354 million) as part of a capital increase but the deal faces an investigation by European Union regulators.

Ryanair is "very interested in getting more slots in Fiumicino, less in Linate because we want to grow in Bergamo and Malpensa," he said.

"To the extent that slots are freed up in Linate, we believe easyJet and Wizz will move aircraft from Malpensa to Linate to take up those slots and that will create more room for us to grow in Malpensa," he added.

"Where ITA isn't growing, Ryanair will grow instead," added O'Leary.

The Ryanair boss said both Boeing and rival Airbus needed to improve the quality of the aircraft they produce.

Ryanair has doubled its team of engineers at the Boeing plant in Seattle after safety concerns this month led to the grounding of 171 Boeing 737 MAX 9 planes.

Europe's largest airline by passenger numbers is one of Boeing's largest customers but operates different variants of the 737 MAX from the type that has been grounded.

"Both Boeing and Airbus have more to do to improve the quality of the aircraft they are making but overall we are very proud to fly the 737, it's a very safe aircraft," he said.

($1 = 0.9184 euros) (Reporting by Angelo Amante Writing by Keith Weir, editing by Cristina Carlevaro, Kirsten Donovan)