Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
operation [ɔpəˈreɪʃən] n (of machine, functioning) рабо́та; (:controlling) управле́ние; (MED, MIL, COMM) опера́ция
to be in operation де́йствовать (impf)
he had an operation (MED) ему́ сде́лали опера́цию
to perform an operation (MED) де́лать (сде́лать perf) опера́цию
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.