Maryland corrections officials and state employe union representatives said they reached agreement tonight to end a sickout by penitentiary guards in the wake of the slaying of a correctional officer at the state's maximum security facility here last Saturday.

Prison officials reported only three of 44 guards failed to show up for the night shift at 8 p.m., compared with 48 of 75 who had failed to report at 8 a.m.. Officials said the massive 1,440-inmate penitentiary near the center of this city was quiet last night.

Leaders of the American Federation of State, County and Municipal Employees, which says it represents a majority of the penitentiary's 380 guards, announced at 7:15 p.m. that about 75 guards voted unanimously at a hastily called meeting to accept a three-point agreement with state officials to end the sickout, which began when some officers failed to report to work at midnight Thursday.

Union and state officials said the agreement package, worked out in daylong negotiations that included direct telephone calls between union officials and Gov. Harry Hughes and state Attorney General Stephen H. Sachs, specified these provisions:

No disciplinary action against guards who participated in the sickout if they report for their regular work shifts beginning at 8 a.m. Saturday.

Appointment by the governor of an independent panel to investigate the security conditions surrounding the fatal stabbing of guard Herman Toulson Jr. by an inmate last Saturday.

Agreement by the state Division of Correction to address a list of guards' grievances to be submitted by the union.

"This is a good package that will allow the guards to return to work with dignity," said Peter J. Moralis, an AFSCME official.

Guards have complained that they are understaffed and need more metal detectors, walkie talkies and other equipment to assure their safety.

Hughes earlier this week pledged an independent investigation of Toulson's slaying. While that idea is now incorporated in the agreement to end the sickout, officials said there had been no specific discussion of the size or composition of the investigation panel.

Sachs said tonight that Hughes had asked him if he would consider heading the panel, "and I said yes." Union officials indicated they favored the idea as well.

Some questions also remain about the scope of the investigation. Union leaders are said to want a broad probe into general security policies at the penitentiary. But Sachs said the state envisions a more limited inquiry that would look at specific "procedures and circumstances that could have caused the condition leading to Toulson's death."

Toulson's death and an emotional funeral service for him earlier this week led union officials to call for the dismissal of prison and state corrections department officials. Sachs said Hughes has refused the demand.

A second union, the Maryland Classified Employees Association, which also claims to represent the bulk of penitentiary guards, has also been involved in the dispute and has condemned prison officials.

Moralis from AFSCME accused the rival union of inciting the sickout. But officials of the Maryland Classified Employees Association denied the accusation, saying the sickout was spontaneous and without union sanction.