The state Senate is expected to vote Tuesday on a plan to draw from a little-known state surplus to help balance the MBTA budget for the year and support public transportation. The plan would send $49 million from motor vehicle inspection sticker fees to the T and $2 million to 15 smaller bus agencies that provide regional transit beyond Greater Boston. The plan would also direct $1.5 million in state highway snow-and-ice removal money left over from a mild winter to the regional bus agencies and $3.5 million to the T.