District Mayor Marion Barry, promising to avoid "even the perception of a risk" to the public, declared a second prison emergency yesterday, and officials said the city plans to start granting early releases today to hundreds of inmates in the city's crowded jails.

"I have taken this extra precaution, legal authority notwithstanding, to ensure that there is not even the perception of a risk to public safety as a result of this management action to reduce prison crowding," Barry said.

Under the mayor's order, officials said, 700 to 800 prisoners will be released before they would normally become eligible for parole. City Corrections Director Hallem H. Williams Jr. said that the early release program will begin today and is expected to be carried out during the next few weeks.

The District's first early release plan, put into effect in July, drew criticism. Officials, including Rep. Stan Parris (R-Va.), charged that the city had violated a commitment to release only prisoners convicted of "nonviolent crimes."

Williams said that District officials have tightened guidelines for early releases and plan to be "very conservative" in deciding which prisoners are set free. To avoid confusion among corrections workers, Williams said, he recently issued a departmental order outlining new procedures for the early releases.

According to Williams, inmates will not be eligible for early releases if they are serving life sentences or mandatory minimum sentences or if they have been convicted of murder, rape, sexual assault, robbery, burglary, arson, kidnaping, extortion or the sale or distribution of illegal drugs.

In declaring the emergency, District officials said that capacity at the city's 10 prisons exceeded court-ordered limits by more than 900 inmates. Under a law that took effect Nov. 14, the mayor can declare a state of emergency and release certain inmates up to 90 days early if the prison system's capacity is exceeded for 30 consecutive days.

As of Nov. 25, corrections officials said, there were 8,043 inmates, a record total, in the city's prisons. The system, which includes the D.C. Jail in Southeast Washington and nine facilities at Lorton Reformatory in Fairfax County, is designed to house a maximum of 7,032, officials said.

Williams said the early release program is considered a "short-term safety valve" to ease prison crowding until a permanent solution can be found. Fewer than 800 inmates may be released under the latest order, Williams said, because some may be turned down by the D.C. Board of Parole.