By Amruta Khandekar and Shubham Batra March 22 (Reuters) - Wall Street's main indexes edged lower on Wednesday, ahead of the outcome of the Federal Reserve's rate-setting meeting in which the central bank will seek to balance inflation and banking sector concerns. Wall Street's main indexes notched gains in the past two straight sessions, after the rescue of Credit Suisse CS.N as well as measures by central banks to boost liquidity helped soothe some worries about risks to other banks. Shares of its peer PacWest Bancorp PACW.Owere down 7.9%, while Western Alliance Bancorp WAL.Nwas marginally up 0.1%.