General Motors agreed to buy a mortgage banker.

In its second major move into the mortgage business this month, GM said it has agreed to buy the Colonial group of companies, a unit of CoreStates Financial Corp. of Philadelphia. The purchase, for an undisclosed price, would make GM the nation’s second-largest mortgage banker. General Motors, the world’s largest car manufacturer, earlier in March agreed to buy the $11-billion mortgage-servicing portfolio of Minneapolis-based Norwest Corp.