WARSAW, May 22 (Reuters) - Poland's top refiner Orlen's first-quarter net profit slumped 70% to 2.77 billion zloty ($704.82 million) on a higher windfall tax impact and weaker refining performance, missing expectations.

Earnings before interest, tax, depreciation, and amortisation (EBITDA) in the quarter fell by 53% year-on-year to 7.73 billion zlotys, while revenues declined to 82.33 billion, the company said on Wednesday. ($1 = 3.9301 zlotys) (Reporting by Anna Koper and Marek Strzelecki Editing by Chris Reese)