The Bloomberg administration has announced an agreement with a group of developers that includes the owners of the Mets to clean up and develop a blighted neighborhood next to Citi Field. The agreement announced Thursday covers a 20-acre portion of Willets Point In Queens. It calls for the developers, Related Companies and Sterling Equities, to construct a mix of retail, hotel and commercial space in a gritty area made up of auto-repair shops and junkyards. Affordable housing units would also be constructed. Bloomberg said the $3 billion project will create 12,000 union construction jobs and 7,100 permanent jobs and will generate $4.2 billion in economic activity over the next three decades. The founders of Sterling Equities are Fred Wilpon and Saul Katz, the owners of the Mets and Citi Field.