The Prince George's County Council voted yesterday to accept a slightly modified version of an executive order that will consolidate child-support collection and enforcement under a single new office.

The council acted despite State's Attorney Arthur A. Marshall's contention that the plan is politically motivated and illegal.

The 6-to-2 vote came after hours of debate and confusion during which County Executive Parris Glendening took part in a round of hurried last minute conferences with his aides and with County Council members.

Marshall, in trying to scuttle the plan, had told the council that he feared the 24 full- and part-time employes who now report to him in his child-support division would be left without jobs if the consolidation went through.

But council members said they felt assured that those employes who wanted to keep their jobs still could if they were willing to transfer out of the state's attorney's office.

"I know where Bud's coming from," said council member Frank Casula, referring to Marshall. "He hates to lose his people. It's a tough decision, Bud, but you're going to have to swallow it."

Glendening's amended executive order, which would have become law on June 4 even without any action by the council, also satisfied opposing council members by providing for their confirmation of the individual who will be selected to head the new Office of Child Support Enforcement.

Marshall said after the vote that his office will no longer contract with the state as it has in the past to perform legal services in child-support cases except where mandated by law.

"Everything will go to the attorney general's office," he said.

Sue V. Mills and Anthony Cicoria, the two council members who voted against the consolidation, agreed with Marshall's point of view.

"In theory, consolidation is a good idea," Mills said. " But it adds to kingdoms, it furthers bureaucracy . . . and it adds to cost."

Glendening has recommended that $3.2 million be spent beginning in July to fund the new agency.

Marshall's argument that the consolidation would be an "unlawful encroachment by Prince George's County into the executive branch of state government" was also rejected last week by Maryland Attorney General Stephen H. Sachs.

Sachs' deputy, Dennis Sweeney, said last week that the state's attorney's role will not be diminished by the consolidation.

In other business yesterday, the council received its first briefing on School Superintendent John Murphy's new plan to meet court-ordered desegregation standards through the creation of magnet schools and the funding of compensatory aid programs for 10 predominantly black schools.

Murphy's presentation met with general approval, even from Democratic State Sen. Decatur Trotter, who previously had termed the magnet school proposal "weak."

"It's a step forward," Trotter said afterward, "but we recognize that it's not a panacea."

Council member Mills, a staunch antibusing advocate during her years on the Board of Education, hailed Murphy's plan as "an idea whose time has come."

But council member Hilda Pemberton voiced the most often heard criticism of the week-old $8.2 million proposal.

"What we are doing with magnet schools is making the black schools better so that you can attract white students who are already doing well," she said.

Instead, Pemberton added, the money should be spent on improving schools for the benefit of the students who are already there.