http://stpetersburg.usconsulate.gov/visas.htmGoogle is your friend, there may be nearer Consulates.
A Visa is required to be in force on entry, not for duration of visit, that is controlled by the I-94.
Here you are:
The visa application procedure for permanent residents of Russia begins at the nearest Pony Express office, where applicants will pay the standard $100 non-refundable application fee in Russian Roubles. Each visa applicant must present a valid travel passport, one 2”x 2” color photo (taken against a white or off-white background within last six months), and a completed and signed Russian or English version of the DS-156 application form. Male applicants between the ages of 16 and 45 will also need a supplemental form DS-157. These forms are available at the Pony Express office, as well as at the front gate of the U.S. Consulate General.
At the Pony Express office, visa applicants will schedule an appointment to appear at the U.S. Consulate General (Furshtatskaya Street, 15; “Chernyshevskaya” Metro). On the assigned date, visa applicants will arrive at the U.S. Consulate General with all supporting documents. After the interview, successful applicants will receive their passports and visas from a Pony Express courier at their home or office address.
Visa applicants who reside outside the city of St. Petersburg should initiate applications through their Northwest Russia regional Pony Express representatives in Arkhangelsk, Vologda, Murmansk, Pskov, Petrozavodsk by calling (800) 200-7669. Residents of Velikiy Novgorod should apply through the Pony Express office at Gzen River Embankment 11, office 410, or by calling (8162) 115167. Applicants from Kaliningrad should apply at Portovaya Street 1 or call (4012) 750896. The handling fee for these applicants is 1300 Roubles per passport.