The Metropolitan Transportation Authority is considering two proposals to shut down the L train tunnel between Manhattan and Brooklyn that would close the subway line under the East River or reduce its service by 80 percent, officials said on Wednesday.

The proposals that will be outlined at a public meeting in Brooklyn on Thursday are closing the entire tunnel for a year and a half to repair damage from Hurricane Sandy, or closing one tube at a time over a three-year period. Any shutdown — a growing source of anxiety among people who live along the crowded subway line — would not begin until early 2019, officials said.

If one tube remained open, trains would run every 12 to 15 minutes, up from the current interval of three to four minutes during the morning rush, officials said at a briefing for reporters. Trains could carry about one-fifth of the 225,000 riders who currently take the L train under the river each day.