The number of American households behind on mortgage payments appears to have reached a plateau at a high level as the economy recovers, a survey showed Wednesday. At the same time, people who fall behind on their mortgages are staying in their homes longer as banks struggle with huge volumes of calls for help and with the complexities of federal and state foreclosure-prevention programs. Diane B. Robertson of Oldsmar, Fla., said she had to stop making mortgage payments around the end of 2008 after a drop in her income. She said her lawyer advised her ‘to just sit tight because you may be sitting there for two years.’ Seventeen months later, foreclosure proceedings are under way, but Ms. Robertson is still waiting to be evicted. The Mortgage Bankers Association, a trade group, reported that 14% of mortgage loans on one-to-four-unit homes were 30 days or more delinquent or in the foreclosure process as of March 31. That represents about 7.3 million households. The rate was 12% a year earlier. BBecky Mehaffey gardens in her yard in Marysville, Wash., on Wednesday. The Mehaffeys are 15 months delinquent on their mortgage but haven’t been evicted from their home. […]