WASHINGTON - Plummeting stock prices. Mortgage lenders filing for bankruptcy or shutting down. Layoffs at homebuilders and banks. Soaring foreclosures and loan defaults. Damage from the nation's slumping housing market is evident throughout the economy and permeates financial markets. Add real estate agents to the growing list of victims, although they know few tears will be shed for them. The National Association of Realtors expects membership rolls to decline this year for the first time in a decade. The group ended 2006 with nearly 1.4 million members — almost double the roughly 716,000 it had in 1997 — but expects...