The embattled administrators of Maryland's prison system attempted today to defuse a consultant's report calling for $311 million in new prison construction by saying it was "only one option" and probably would not be needed.

Corrections Secretary Gordon Kamka and Prison Commissioner Edwin Goodlander argued that they already are "the biggest prison-building administration in the country" and that a consultant's conclusion that at least 926 more prison beds would be needed by 1990 was bases on shaky assumptions.

They spoke to a roomful of legislators from the House Appropriations Committee who have long opposed their policy of emphasizing community-based institutions over medium-and maximum-security prisons.

The consultant's report, prepared for the legislature by the Kansas City-based Correctional Services Group at a cost of $100,000, has prompted a sudden new controversy in the legislature over the state's prison construction program. The consultants argued that despite the two new prisons authorized by the legislature last year, Maryland will face the same over-crowding problems in 1990 that it has now unless it begins work immediately on more new prisons.

As a result, angry legislators are saying that Kamka and Gov. Harry Hughes made a mistake when they dropped plans to build an 890-bed prison in Baltimore two years ago. Several members of the committee, which heard both the consultant's report and administration's response today, say they are considering introducing legislation this session for planning and design funds for a new 600- to 800-bed prison.

Such a proposal would certainly be opposed by Hughes and Kamka. Kamka, who appeared sullen today as hostile delegates needled him over the prison system's problems, left most of the responses to his deputy, Goodlander.

"I'll tell you what the prison population will be in 1990," Kamka told the committee at one point as he was questioned about projections. "It will be whatever number of beds we decide to build."

Goodlander maintained that the consultant's projection that 926 more beds than now planned would be needed was based on proposed changes in policy that prison administrators do not want to make.

For example, he said, the consultant recommended that 10 percent of each prison be left vacant in order to insure proper management of inmates. "This is a very costly proposition," said Goodlander, adding that only 3 to 5 percent of each prison's capacity should be vacant at any time.

If such assumptions of policy changes are eliminated from the consultant's report, Goodlander argued, the state would have a surplus of prison beds in 1990, not an overcrowding problem.

Goodlander also disputed as "arbitrary and unfair" the consultant's conclusion that one-third of inmates assigned to prerelease centers belonged in more secure settings.

The consultant said the state should adopt a standardized, objective system for assigning prisoners to various security settings, but Goodlander insisted such a change would be "fraught with problems" and that "the staff's subjective opinion and experienced discretion are important to the classification process." He added, however, that the state would accept the consultant's suggestion that four levels of security be adopted for inmates, rather than the current three, separating minimum security facilities into two levels.

None of the prison administration's critics, who have jousted in such hearings with Goodlander and Kamka for three years in a row, seemed to accept their defenses today.

"Since you're talking about subjectivity in classification," Del. Timothy Maloney (D-Prince George's) told Goodlander, "you should know that most of the people associated with the criminal justice system in Maryland subjectively believe that those people being released [from state prisons] don't belong on the street."

The legislators' fuming over the consultant's report comes shortly after the state told a federal judge last week it would be forced to miss another deadline for ending overcrowding in prisons because of delays in the construction of two new prisons. The new facililties were supposed to be finished April 1 in order to allow the transfer of hundreds of inmates out of overcrowded cells at the Maryland Penitentiary in Baltimore and the Maryland Correctional Institute in Hagerstown by April 15. They will not be ready until the end of May, state officials said.