Prince George's County will receive an unexpected $1.5 million from the Maryland Department of Transportation, which has refinanced $155.7 million in road and highway bonds and returned a $3.3 million saving to 15 local jurisdictions.

But the real financial benefit in Transportation Secretary William K. Hellmann's plan will go to Baltimore.

The city helped work out the refinancing scheme and will save nearly $20 million that it had planned to spend on debt repayments between now and 1993. Such bonds are sold by the state for the benefit of localities.

"It's like finding money in the street," said Senate transportation subcommittee Chairman Frank Komenda (D-Prince George's).

County officials said that the extra money, which had not been included in budget estimates, will be reserved until next year to offset an expected $22 million revenue shortfall.

However, Del. Timothy F. Maloney (D-Prince George's), who chairs the House transportation subcommittee, said that the money should be reserved for magnet school spending because that remains the county's top legislative priority for the 1986 session.

"I can't imagine that the money would be used for anything other than magnet schools," he said.