Maryland Gov. Harry Hughes, who after winning reelection to a second term last fall predicted few defections from his cabinet, is now scrambling to fill four major posts in his administration, after having filled two others this year.

The governor said last week that the turnover--six out of 13 cabinet secretaries--is not a sign of trouble in his administration.

"It's normal when you have very good people at the top of your departments. They know this is my last term and they have their futures to think of," Hughes said.

Maryland allows governors to serve only two consecutive terms.

The governor and his staff said they expect the vacancies to be filled soon. A new secetary of public safety and correctional services is expected to be appointed by the end of this week, according to Hughes aides.

Immediately after his November reelection Hughes was forced to find a replacement for Secretary of Human Resources Kalman Hettleman, who announced he was retiring because of the fatigue of government service.

Shortly after that Hughes had to find a new secretary of natural resources.

Since then the head of the state's troubled penal system, Thomas Schmidt, and Secretary of Health and Mental Hygiene Charles R. Buck Jr., announced they were leaving. Buck's deputy, who was the leading contender for the health post, also announced his imminent departure.

On Saturday, Hughes named J. Max Millstone, who had been secretary of the Department of General Services under five governors, to the Workmen's Compensation Commission, creating yet another cabinet vacancy.

In addition, the creation of a new Department of Employment and Training means that Hughes must find a person to run that agency.

The governor and his aides said that the high-level personnel changes will not bring about any fundamental changes in the way the agencies or the Hughes adminstration is run.

The one exception will be in the prison system.

Until three years ago Maryland's prison system was run by Gordon Kamka, a young Baltimore reformer who emphasized rehabilitation programs and putting prisoners into community-based programs.

Kamka appeared to lose control over the system as one incident or breakout followed another, and became a source of continual and growing political problems for Hughes.

In 1980 Kamka resigned under fire and was replaced by Schmidt, who backed away from rehabilitation and moved toward a lock-'em-up, build-more-prisons philosophy.

Although Schmidt solved many of the management problems in the overcrowded system, Hughes, a liberal Democrat, reportedly has grown unhappy with the abandonment of rehabilitation.

But wary of the political furor that such words as rehabilitation have among legislators concerned about law and order, Hughes aides say the next prisons chief must have good management skills like Schmidt's, but should be willing to bring back some of the emphasis on education and programs dropped under fire several years ago.

"There's been a tremendous pendulum swing from no-build to tightening everything down," said one administration official. "We want the pendulum to settle down in the middle. You have security but you start preparing people to go out into the world."

The governor is considering five candidates for the corrections post and is scheduled to finish interviewing them early next week.

Among the possiblities, three are from out of state and all would be categorized as "moderates," officials said. One conservative initially under consideration, Raymond Procunier, who quit under fire last week as director of corrections in Virginia, was eliminated as a possibility before that, officials said.