Maryland's commissioner of consumer credit has launched as investigation into the allegedly "sky-rocketing costs" consumers must pay when their cars are repossessed by credit companies, an agency spokesman announced yesterday.

One Prince George's County man recently was charged more then $1,800 for the "retaking, storing and sale" of his repossessed 1976 Ford Granada.

He had owed about $2,800 on the car before it was repossessed. It was sold by the credit company for about $2,400 - which would have left him owing only $400 if the resale price had been applied to his car payments. Instead the man ended up owing more than $2,200 when other costs were added in.

"On the face of it, that looks awfully high," Commissioner Alan T. Fell said of the repossession costs. "It needs to be looked into carefully when a man can find himself almost as deep in debt after the car is resold as he was before it was repossessed."

The Prince George's example was culled from the commissioner's recent files on the Wheaton branch of the Ford Motor Credit Co., a national firm that provides car loans. All credit companies must file statements of repossession sales with Fell's office.

Fell said he is starting his investigation with the files, of the Ford Co., a subsidiary of the Ford Motor Co., but he stressed that the higher repossession costs are "an industrywide trend."

A spokeman for the Ford Motor Credit Co., in Dearborn. Mich., said he could not speak specifically about the Prince George's County example because the files were not available. But he said there are "a wide variety of factors" that could add to the repossession costs.

These include the use of an investigator to locate a car, costs to recondition or repair it and the payment of a repair bill in order to obtain release of the car from a garage, according to spokesman Thomas Foote.

George L. Rayburn. the assistant commissioner of consumer credit, said that before the recent in creases repossession costs had ordinarily been running around $200.

But an informal survey of about 45 Ford Motor Credit Co., statements in recent months from its Wheaton office showed that in only four cases did the costs run below $300. Costs for "retaking and storage" on these statements ranged from $4 in one case to more than $1,900 in another. "Sale expenses" ran from $4 on the sale of a repossessed 1976 Mustang to more than $600 for a 1974 Mustang.

Fell said that most consumers do not realize that they will be charged for any payments or repossession costs that are not made up by the resale of the auto, usually at an auction.

But a consumer is notified by mail, once his repossessed car has been solad that, of whatever remaining charges he owes.

"The only shot he has got to fight this is to go into court after that letter comes," Fell said. He urged consumers to call his office or go into court if they feel the charges are too high.