Big health insurers have punched up lobbying spending this year as the debate over a potential overhaul of the nation's health care system heats up in Washington.

The five largest private insurers and the trade group America's Health Insurance Plans spent a total of $6.4 million in the first quarter, an increase of more than $1 million from the same quarter last year. The industry is working to counter proposals endorsed by the White House that would offer a government insurance option for millions of Americans.

Individually, Minnetonka, Minn.-based UnitedHealth Group Inc. spent $1.5 million in the first quarter, up 34 percent from $1.1 million in the same quarter last year. Hartford, Conn.-based Aetna Inc. spent $809,793, up 41 percent from last year.

Indianapolis-based WellPoint Inc. and Louisville, Ky.-based Humana Inc. both saw first-quarter spending rise 16 percent to $1.2 million and $370,000, respectively. Spending for Philadelphia-based Cigna Corp. nearly doubled to $450,000 in the first quarter from a year ago.

Insurers lobbied on an array of issues in the first quarter amid a heavy legislative agenda. Those included the expansion of a health insurance program for children and subsidies that help people retain their employer-based health insurance if they lose a job.

But a spokesman for America's Health Insurance Plans, which represents about 1,300 insurers, said its main focus was ensuring its members' voices are heard on Capitol Hill in the health care reform debate.

"Right now, we are putting all of our resources behind building support for comprehensive health care reform," Robert Zirkelbach said.

The association spent more than $2 million on first-quarter lobbying, according to a report filed last month. That's a 12 percent increase compared with last year.

President Barack Obama has called for an overhaul of the U.S. health care system to cover the uninsured and rein in costs. Obama and many Democrats in Congress say a government insurance option would help keep the private insurance industry honest.

But insurers have said such government competition would hurt employer-based health coverage and make it harder to reform the overall system. They also worry that it could hurt them if the government option competes for the business of middle-income Americans.

Insurers favor an overhaul that offers coverage for everyone by improving and expanding existing elements of the health insurance system.

A federal entity that also provides coverage may show that private insurers aren't as necessary, said Etti Baranoff, an insurance and finance professor at Virginia Commonwealth University, who wasn't surprised that private insurers spent more on lobbying so far this year.

"They now have to really guard what they have, and there is a feeling that they could lose ground," she said.

The health care debate wasn't the sole reason for spending to increase. An Aetna spokesman said his company's first-quarter spending rose mainly because it made dues payments to industry trade associations.