The Virginia Housing Development Authority turned in the best showing in mitigating losses on FHA-insured single-family mortgages among the 50 largest servicers involved in this market, according to new data released by the Department of Housing and Urban Development. The state agency, which services a relatively small portfolio of 13,782 FHA loans, performed considerably stronger than its peers in the "medium high volume" category of servicers on the two basic measures considered by HUD. Those