ST. LOUIS (AP) – Ameren Corp. executives have said two massive power outages in the last four months were not preventable, but an Illinois commission warned last year that cuts in tree-trimming might lead to such problems, according to a published report.

A July windstorm and a winter storm that began Nov. 30 left more than 500,000 homes and businesses without power in Missouri and Illinois.

St. Louis-based Ameren said both storms were so severe that the company couldn’t have done anything to keep power on. But an engineer with the Illinois Commerce Commission said Ameren’s tree-trimming program did not meet state standards, the St. Louis-Post Dispatch reported Sunday.

Jim Spencer, a senior electrical engineer for the Illinois commission, inspected Ameren’s power lines in 2004 and 2005. The company operates power in Illinois under its subsidiary, AmerenIP.

Spencer wrote in a letter dated Aug. 17, 2005, that Ameren’s tree-trimming efforts were inadequate.

“Based on the evidence in these two areas of AmerenIP’s service territory, I have no reason to believe that Ameren has applied the resources necessary to adequately recover from its deficient tree trimming program noted during my inspections of a year ago,” he wrote.

Ameren spokeswoman Susan Gallagher said in an e-mail that the company adheres to the four-year tree trimming cycle mandated by the ICC.

After analyzing the July blackout, Missouri’s Public Service Commission recommended that Ameren boost its tree trimming program. In 2004, the PSC said the program was inadequate because of budget cuts.

Because of the findings, Ameren increased its budget to $32.2 million from $23.5 million and is on schedule to meet state requirements by December 2008, according to the PSC.

Both Missouri and Illinois officials have criticized Ameren’s response to the most recent blackout

Missouri Gov. Matt Blunt asked the state’s Public Service Commission to hold public hearings and said he wants Ameren to provide a clear plan for preventing a recurrence. Illinois Lt. Gov. Pat Quinn also pressed utility regulators to investigate, calling the power disruptions a “systemic failure,” despite the efforts of thousands of repair workers from 14 states.