A key Virginia legislative committee, in a rebuff to Gov. Charles S. Robb, today refused to go along with his plan to slash hundreds of jobs in the state's colleges and rejected his call for an immediate pay increase for prison guards.

The House Appropriations Committee, citing studies finding widespread mismanagement in the state's prisons, called the governor's plan to give the raises in April unrealistic and questioned Robb's approach to resolving other prison problems.

In another surprise move, the committee approved a 12.5 percent increase in the Aid to Dependent Children assistance program, more than doubling Robb's recommended 5 percent increase.

Robb's proposal would have raised payments for the average ADC family -- a mother and two small children -- by $13 a month. The committee's action would give the same family about $30 more each month.

The committee, which completed its work on a $290 million amendment to the state's biennial budget today, recommended tying guard pay raises to new programs for improving their recruitment and training.

The panel reluctantly endorsed Robb's plan to transfer 57 state mental health department positions into the prisons.

The legislators moved to restore 349 of 625 positions that Robb had asked to be cut from the state's college system, one of the most controversial proposals in the governor's budget amendments. Most of the cuts would have come in the state's struggling community college system, which has suffered sharp enrollment declines.

"We present this recommendation as our 'best shot' at dealing with an issue that has no easy answers," the committee said.

The panel restored most of the 145 positions that would have been cut from the Northern Virginia Community College, the largest in the state.

Projects in the Washington suburbs won several major appropriations from the committee, including $4 million to pay for the design of a new midfield terminal at Dulles Airport, as well as money for jail construction, community mental health programs and more state police to patrol suburban interstate highways.

"We made out like bandits," said Del. Robert E. Harris (R-Fairfax), a member of the appropriations committee. "But we have to be humble about it."

The pay package approved by the committee after two weeks of hearings is part of the overall adjustments the legislature will be asked to make to the state's $16.5 billion biennial budget approved in 1983. Most of the money being spent by the assembly comes from last year's $81 million surplus, an unexpected rise in the state's sales tax revenues and budget reductions imposed on several state agencies.

In addition to the House changes, the Senate Finance Committee is expected to finish work on its version of the budget Sunday night. The proposals from each side then will be worked out in a conference committee before Feb. 23, when the session is due to end.

A series of escapes and inmate disturbances during the past nine months prompted Robb to list the state prison system as one of his top financial priorities for this session.

But many lawmakers have said they are hesitant to funnel more money into the prisons before uard training and management of the corrections department are upgraded.

The legislative committee approved almost $2 million for security improvements and additional equipment for guards.

In other areas, the panel recommended spending $350,000 to redecorate the House of Delegates chambers, $789,000 for local jail construction in Northern Virginia and other areas and $50,000 for a new oyster hatchery to study methods of increasing oyster yields.