Gov. Charlie Baker is seeking federal disaster relief for six Massachusetts counties hit hardest by the March 2-3 nor'easter that pounded the region with hurricane-force wind and rain and downed trees.The Republican governor on Monday asked the Federal Emergency Management Agency for a major disaster declaration for Essex, Plymouth, Norfolk, Bristol, Barnstable and Nantucket counties.Baker said preliminary estimates show emergency protective measures, debris clearance, and repairing or replacing damaged public infrastructure exceed $23.8 million - well beyond the statewide threshold of $9.5 million.Baker is also seeking a disaster declaration from the federal Small Business Administration.The declaration would let the agency make low-interest home disaster and business physical disaster loans available to eligible applicants in Norfolk County and neighboring counties including Plymouth, Bristol, Suffolk, Middlesex and Worcester