For more than 20 hours each day, Cecil Washington sits locked in his 6-by-8-foot cell in Cellblock of the Lorton prison's maximum security unit while hundreds of other inmates walk about the prison grounds.

He can shower only three times a week, and must eat all his meals within four feet of the toilet in his cell. He is not allowed to participate in job programs in the prison, exercise outdoors, or go to the prison's law library or commissary.

Cecil Washington did not lose his prison privileges for being a troublemaker. Instead, he is one of 78 persons housed in "protective custody" at Lorton because of assaults and real or perceived threats of assaults from other inmates.

Washington is one of three inmates who filed suit in U.S. District Court here yesterday charging that they are unconstitutionally denied prison privileges that are freely available to other, more dangerous inmates. Washington described his situation in an affidavit filed with the suit.

The proposed class action suit, filed by attorneys Andrew S. Krulwich and Paul W. Sweeney Jr. of the prestigious District firm of Arnold and Porter, asked that the inmates in "CB-5" be held in conditions that are "substantially equal to those in the general prison population."

The suit follows two years of sporadic correspondence between Public Defender Service attorneys and D.C. Corrections Department director Delbert Jackson concerning the conditions under which Lorton inmates are held in protective custody.

In one letter made public yesterday, Jackson told the attorneys for the inmates that they had been "misled" as to the nature of the special confinement and suggested that inmates are kept there because they refuse to identify the inmates they fear or because their fears are "imaginary."

"I agree that the programs and activities available to these men are limited because of concern for the safety of the men," Jackson said in the Oct. 8, 1975, letter.

In December, 1975, Jackson rejected an attorney's list of specific proposed changes for the handling CB-5 inmates as being "without merit or . . . not administrable."

The CB-5 inmates claim in their suit that they are kept in conditions that are even more strict than conditions for inmates who are being punished for prison violations or are considered dangerous.

For example, the inmates claim in the suit that half of the persons imprisoned in CB-5 literally "never have an opportunity to see the outside world" because of the configuration of the cells there.

Washington claimed in his affidavit that he requested security after he refused to participate in an inmate work strike in the culinary unit where he worked. He said he was threatened by other inmates because of that refusal, and transfered to CB-5.

Since being in CB-5, Washington said, he has lost access to rehabilitative programs and cannot earn extra money or participate in college-level study programs as other inmates do.

He said the heating and cooling systems are defective in the cellblock, that he is limited in his contracts with visitors, and even restricted in the amount of clothing and blankets he can have in his cell.

Another inmate, Edward B. Williams, said he was transferred to CB-5 after he was attacked and robbed of a ring by three inmates carrying homemade knives. After he identified the inmates, he said, prison officials told him "these inmates had many friends in the general population of the institution and that I would probably be safest if I was confined in CB-5."

One prison guard captain expressed his regret at a hearing on the transfer that Williams "would be the person to suffer because I was the victim of an assault," Williams said in an affidavit.

The third inmate named in the suit yesterday was former metropolitan policeman Larry Sutton, who said he was placed in the protective confinement area by prison officials because of his former employment.

He said his place of confinement is blocking him from an early parole, because one of the specific conditions of his parole eligibility is that he receive psychiatric counseling. Such counseling is not available to him in the CB-5 unit, he said.