WASHINGTON — The US economy grew unevenly in early fall, with more than half the regions of the country expanding modestly while others are struggling to grow.A survey by the Federal Reserve released Wednesday found that seven of the Fed's 12 regions reported moderate improvements in business activity. Three regions — Philadelphia, Richmond and Cleveland — described economic activity as mixed or steady. Only two regions — Atlanta and Dallas — suggested economic growth was slow.The survey indicated that the economy isn't weakening but is growing too sluggishly to drive down high unemployment, now at 9.6 percent. The jobless rate has been at or above 9.5 percent for more than a year."Hiring remains limited, with many firms reluctant to add to permanent payrolls given economic softness," the Fed survey concluded.