LYNN – It took firefighters an hour to knock down a suspicious blaze at 68 High Rock St. Wednesday morning but fires in foreclosed properties like that one and others across Lynn have become a constant worry for fire officials.District Fire Chief Thomas Swirka said investigators are focusing on the three-story building’s basement and the likelihood the fire was deliberately started.The property was advertised for foreclosure sale in February and a representative of a company hired to manage the building was visiting another foreclosed Highlands property when she spotted one of 68 High Rock’s rear doors open shortly after 8 a.m.”Someone was here,” Swirka said.The building was the second fire in the city in as many days with firefighters extinguishing a car fire that damaged a house Tuesday at 64 Eutaw Ave.Swirka said the Fire Department has pages of addresses for vacant, foreclosed properties catalogued by city inspectors.Foreclosed, often abandoned homes are a growing problem for municipalities like Lynn and Revere where inspectors are fielding neighbors’ complaints about uncut grass and trash even as they attempt to track down banks and absentee owners.In the first half of the year, Lynn logged 144 home foreclosures with two-family homes accounting for 54 recordings with the Southern Essex Registry of Deeds.City inspectors call them “walk aways” and Lynn ordered 10 foreclosed properties boarded up in the first half of the year at a cost of $1,200 to $1,500 a home.City inspectors attempt to contact the former owner or the mortgage holder before posting the property for cleanup and sending a letter to notify the bank or owner that the residence will be secured.The inspection chiefs said their challenge is to get banks and other mortgage holders to hire local contractors to secure and keep an eye on vacant foreclosed homes.