Health insurer Anthem Blue Cross will postpone its much-criticized plan to raise rates for some California residents who buy insurance on their own, after reaching a deal Saturday with state regulators.

Anthem’s planned rate hike, which the state estimates would affect about 700,000 customers, averaged 25 percent and would have been as high as 39 percent for some.

Anthem Blue Cross of California, based in Thousand Oaks, agreed to postpone the increase from March 1 until May 1 so California could have outside experts review the company’s complex and detailed plan filing, including data on the medical costs it expects to incur.

The California Department of Insurance had been working with Anthem since mid-November to get more information about the increase, Insurance Commissioner Steve Poizner said. He wanted to have experts comb through the company’s figures to confirm the new rates comply with a 2006 state law that insurers spend 70 cents of every premium dollar on medical care.

“Medical cost inflation in California is in the 10 to 15 percent range, so I have a healthy skepticism how they can get to 39 percent” and comply with the law, Poizner said.

If they don’t, he said, he will direct the company to reduce its prices, “or I will take away their license to sell insurance” in California.

He officially requested the delay Monday, but said Anthem stuck to its position that the individual insurance plan had lost money last year and the rate increases were justified — until Saturday. The change of heart came after a week of extensive media reports about the rate hikes, harsh criticism from the Obama administration and two Congressmen scheduling a hearing to look into the rates Feb. 24.

Anthem, a subsidiary of insurance giant WellPoint Inc. of Indianapolis, said its proposed rates reflect anticipated medical costs.

Health and Human Services Secretary Kathleen Sebelius said Thursday “it remains difficult to understand” how premium increases of that size can be justified when WellPoint Inc. reported a $4.75 billion profit in the last quarter of 2009.

“While a two-month delay offers some temporary relief, what California families need is long-term health insurance security, so that they don’t face sharply higher prices or fewer benefits,” Sebelius said Saturday. “This rate increase underscores the urgency of passing real health insurance reform.”