The U.S. government has increasingly relied on food-safety inspections performed by states, where budgets for inspections in many cases have remained stagnant and where overburdened officials are trained less than their federal counterparts and perform skimpier reviews, an Associated Press investigation has found.

The thoroughness of inspections performed by states has emerged as a key issue in the investigation of the national salmonella outbreak traced to a peanut processing plant in Blakely, Ga. The outbreak, which has highlighted weaknesses in the nation's food-safety system, is blamed for 600 illnesses and at least eight deaths in 44 states.

The House Energy and Commerce investigations subcommittee, which is to hold a hearing Wednesday on food safety, scheduled a meeting Tuesday to issue a subpoena for Peanut Corp. of America President Stewart Parnell, said a senior aide to a member of the panel. The aide, who spoke on condition of anonymity because panel members were still being notified, said Parnell was otherwise refusing to appear at the hearing.

State investigators performed more than half the Food and Drug Administration's food inspections in 2007, according to an AP analysis of FDA data. That represents a dramatic rise from a decade ago, when FDA investigators performed three out of four of the federal government's inspections. The Agriculture Department is responsible for meat and dairy safety.

Increased inspection responsibilities have not been accompanied by big spending increases in many states responsible for the bulk of the nation's food production.

The FDA covers some costs for states to perform inspections. But in Pennsylvania and Ohio, for example, each state's own food safety spending increased only slightly since 2003, less than the rate of inflation; in California and Massachusetts, just barely more than inflation; and in New Jersey, spending has remained about the same. Those are among states with the largest numbers of food-processing plants.