The international terrorist known as Carlos, gray-haired but proudly boasting of being ''a professional revolutionary in the old Leninist tradition,'' went on trial here today on charges of killing two French security officials and a Lebanese informant 22 years ago.

Carlos, a 48-year-old Venezuelan named Ilich Ramirez Sanchez who enlisted in the Palestinian cause after a Marxist upbringing and an education in Moscow, has spent more than three years in French jails and is wanted by at least four other countries for kidnappings, killings and bombings in the 1970's and 1980's.

He was convicted in absentia by a French court in 1992 and sentenced to life in prison in the same 1975 case for which he is now being retried.

Carlos became entitled to a new trial after French agents tracked him down to a hideout in Khartoum, the capital of the Sudan, in the summer of 1994 and persuaded authorities there to let them take him to France, just after he had undergone a minor operation.