BANGKOK, July 17 (Reuters) - The Thai industrial sentiment index fell for a third straight month to its lowest in two years in June due to a slow economy, weak demand and bad debt problems, the Federation of Thai Industries (FTI) said on Wednesday.

The FTI's industrial sentiment index dropped to 87.2 in June from 88.5 in May.

Meanwhile, political uncertainty dented confidence of business operators, while smaller firms faced liquidity problems as banks tightened lending, the FTI said in a statement.

Prime Minister Srettha Thavisin faces a Constitutional Court case that could potentially lead to his dismissal. He denies wrongdoing and the court's next hearing in the case is July 24.

The FTI said tourism, a major driver of Thai growth, continued to support the economy.

Thailand received 18.9 million foreign tourists from the start of the year to July 14, up 34% year-on-year, with about 3.7 million of those Chinese, government data shows.

The government has forecast Southeast Asia's second-largest economy will grow 2.5% this year, after expanding 1.9% last year which lagged regional peers. (Reporting by Kitiphong Thaichareon; Writing by Orathai Sriring; Editing by John Mair, Martin Petty)