Matthew Staver/Bloomberg via Getty Images WASHINGTON -- More Americans signed contracts to purchase homes in April than the prior month. But the pace of buying is still weaker than last year, as higher prices and relatively tight supplies have limited sales. The National Association of Realtors said Thursday that its seasonally adjusted pending home sales index rose 0.4 percent to 97.8 last month. The index remains 9.2 percent below its level a year ago. Pending sales are a barometer of future purchases. A one- to two-month lag usually exists between a signed contract and a completed sale. The index indicates that home buying has barely increased in May. The gain in signed contracts partly reflects the slight decline in mortgage rates and the economic rebound from the brutal winter. But prices have risen by 12.4 percent year-over-year, according to Standard & Poor's/Case-Shiller 20-city home price index. That has put home ownership out of reach for a growing share of Americans who are stuck with stagnant incomes in the aftermath of the Great Recession. The number of signed contracts increased in the Northeast and Midwest month-to-month, suggesting that a modest weather-based rebound has occurred. However, pending sales dropped last month in the West and South, a sign to many economists that the price increases have muted buying activity more than nasty weather. "The end of the severe winter weather will not bring with it a sustained revival in the housing market," said Ian Shepherdson, chief economist at Pantheon Macroeconomics. "The real problem is last year's massive deterioration in affordability." Would-be buyers have gotten some help in recent weeks from falling mortgage rates. Average rates for 30-year, fixed mortgages declined for the fifth straight week to 4.12 percent, according to mortgage buyer Freddie Mac. Still, rates remain above their lows of 3.51 percent a year ago. The rising rates in the second half of 2013 and higher home prices appear to have reduced the pool of potential homebuyers. The Realtors said last week that sales rose 1.3 percent in April from March to a seasonally adjusted annual rate of 4.65 million. Purchases of homes over the past 12 months have dropped 6.8 percent.