Signaling that the worst of the housing mess isn’t yet behind us, the number of homeowner vacancies reached a new record high in the first three months of 2008, according to data released Monday morning by the U.S. Census Bureau. Homeowner vacancies crept up to 2.9 percent of total by the end of March, up slightly from the 2.8 percent rate recorded during the first and fourth quarters of last year. Rental vacancies crept upward as well, rising to 10.1 percent from 9.6 percent one quarter earlier, and matching the rental vacancy rate recorded to start 2007 and 2005. A total of 18.6 million properties sat vacant in the first quarter, up one million from year-ago totals. Rising inventory — which translates into increased homeowner vacancies — is a strong signal that housing has yet to balance itself out, according to most major housing experts; a growing inventory overhang is seen by many as the single largest hurdle to any recovery in the U.S. housing market. Homeowner vacancies were concentrated most in principal cities, the Census Bureau said, at 4.3 percent; suburbs and areas outside MSAs reported homeowner vacancies of 2.5 and 2.3 percent. The Western region of the U.S. saw homeowner vacancies increase rather sharply, up to 3.2 percent from 2.6 percent one quarter earlier — bringing the West into a tie with Southern U.S. states for the most homeowner vacancies in the nation. Despite increased vacancies, the homeownership rate increased slightly in the first quarter to a seasonally-adjusted 67.9 percent, up from the 67.7 percent recorded in the fourth quarter — but still off from the 68.5 percent recorded one year ago.