St. Louis Mayor Francis Slay and city law enforcement plan to ask for 400 National Guard troops to augment the city’s police force following the announcement of the St. Louis County grand jury’s decision regarding the Ferguson police shooting.

Slay told the city’s Board of Aldermen in a letter released Tuesday night that the Guard troops would be split into two groups, each of which would work 12-hour shifts.

He said the troops would be stationed throughout the city at 45 locations. But he added, “We will not, unless something happens that we have not foreseen, post them where there are organized protests.”

Slay offered the most detailed information to date regarding numbers of National Guard troops and plans for their deployment. Missouri Gov. Jay Nixon, who called up the Guard, told reporters in a conference call Monday that he would not release details on how many Guard troops have been called up and where they would be deployed.

County officials also have declined to provide any information about law-enforcement plans.

Nixon has declared a state of emergency, in preparation for possible unrest following the grand jury’s announcement of whether it will recommend that Ferguson police officer Darren Wilson be indicted for the fatal shooting of unarmed teenager Michael Brown on Aug. 9.

Many public officials expect that the grand jury will not support an indictment, which is expected to touch off protests from Brown supporters.

Slay also told the aldermen that some area churches will be designated as “sanctuaries’’ for protesters, where police will not enter. The only such church in the city, he said, is St. John’s Episcopal Church, 3664 Arsenal Street.

Slay added in the letter that city Police Chief Sam Dotson and other regional law enforcement officials have met with representatives of some of the protest groups, and have agreed to at least half of the group’s proposed 19 rules of conduct.

Slay did not specify which of the proposed "rules’’ have been agreed upon, and which ones have not.

The mayor added, “I am absolutely convinced that the leaders of the demonstrations and the vast majority of demonstrators themselves are committed to nonviolence.”