Mayor Marion Barry yesterday backed down from his original plan to lay off 150 prison guards and 75 other employes of the D.C. Corrections Department, and instead dismissed only 76 workers -- 31 guards and 45 others.

City Administrator Elijah B. Rogers said final layoff notices went to the 76 employes yesterday. Today is their last day of work, Rogers said. No further layoffs in the department are planned for this fiscal year.

Since Barry announced his intension to lay off 150 guards and 75 other workers in March, the plan has been the subject of legal challenges and community concern.

Inmates successfully blocked any reduction in force at the maximum security facility at Lorton Reformatory by asserting successfully in U.S. District Court that decreasing the number of guards would endanger the safety of inmates and guards. The guards themselves filed suit in Superior Court in an unsuccessful effort to block all the layoffs.

Last Tuesday night, about 40 persons who live near the D.C. Jail in Southeast gathered at the District Building to talk to Barry and other officials about jail security in the wake of a four-man escape two months ago. One of the issues discussed at the meeting was the lay-off plan, which some residents fear will lower the level of security at the jail.

Guards threatened earlier in the week to begin performing all their tasks "by the book" -- that is, meticulously conducting searches and examinations that usually are done quickly or not at all.

The action would have amounted to a work slowdown. However, corrections officials said yesterday that the slowdown never materialized, and operations at all facilities have remained normal.

Yesterday's announcement signals a further erosion of Barry's original plan to help balance the city's budget, which faces a deficit for the current fiscal year of up to $170 million. The Corrections Department had been targeted for the lions' share of 403 layoffs citywide.

The decision to cut the corrections layoffs by two-thirds is a further indication that this year's budget will not balance -- a fact that officials have all but admitted.

Rogers said the number of layoffs was reduced because the attrition rate in the department has been greater than expected. Since February, Rogers said, 110 jobs have been vacated through attrition.

But he indicated that the administration in formulating the original plan, already had planned to lose more than 70 jobs through attrition. Rogers said that controls on department spending have produced enough additional savings to slash the planned layoffs to the levels announced yesterday.

Stuart Kirsch, staff counsel of the American Federation of Government Employees -- which represents the workers -- said his union had mixed reactions to Rogers' announcement.

"We're glad they recognized the serious deficiencies that would have been created by servere reductions in force," he said. "On the other hand, we're displeased with any reductions because the jails are already understaffed."

Kirsch said the union probably would seek to challenge the way the 76 employes are being laid off. The city had told a number of department workers that they would be laid off last Monday, then called them back and told them to continue working for the rest of the week.

Kirsch said the union believes the city should have to issue new 30-day layoff notices to all 76 workers "so they can make arrangements for other jobs." But Rogers contended there was no need for another 30-day period.

Kirsch said the union is "still considering" an appeal of the Superior Court ruling against the suit to block any department layoffs.

William D. Golightly, assistant director of the department, said the employes to be laid off are among the last hired.

He said the department will abide by a U.S. District Court order to station at least 152 guards at the Lorton maximum-security facility.

Workers to be laid off include some high-paid employes, such as three jail administrators and two computer specialists.