The Friday blaze at the Trinity Cathedral led to the collapse of the main 80-meter-high dome and damaged four smaller blue domes. Precious relics inside the 19th-century cathedral, which is on the Unesco World Heritage List as part of St. Petersburg's historical center, were saved.
"Studies and estimates have to be made now to carry out a massive restoration effort next year, which must be completed no later than next fall," Valentina Matviyenko said.
Museum officials in the city earlier expressed concern about financing the restoration efforts at the major city landmark, which was under scaffolding when the fire broke out.
The head of a local museum protection watchdog, Vera Dementyeva, said in the immediate aftermath of the fire that the reconstruction would take about eighteen months, adding this was only "possible given normal financing."
Matviyenko threatened last week to fine the restorers, who were still working in the cathedral, if they were found to have caused the blaze.