WASHINGTON — The nation's most powerful network of seniors today will join the nation's most powerful network of drugmakers in combat over rising drug prices.

The nearly 38 million-member AARP is launching newspaper and radio advertisements in 10 states urging the Senate to pass legislation that would give the federal government the power to negotiate for lower prices in Medicare's prescription-drug program.

Ads will run in the Washington, D.C., area and in states from New Hampshire to Alaska, strategically chosen in an effort to influence senators whose votes could make the difference. They will clash on the airwaves with the drug industry's ads opposing the legislation, which have run on television since before the House approved similar legislation in January.

The battle over the government's ability to influence drug prices comes nearly four years after Congress approved the Medicare prescription-drug program in 2003. The program, which began last year, initially dropped or overcharged millions of low-income seniors and people with disabilities. Now, more than 90 percent of Medicare beneficiaries have drug coverage and save an average of $1,200 a year.

To control costs, Congress created a gap in coverage during which beneficiaries pay the full cost of their drugs. The gap, known as the "doughnut hole," begins when a participant's total drug costs have reached $2,400 and continues until they have paid $3,850 on their own.

As seniors' drug prices rise at twice the rate of inflation in many cases, the two sides have squared off over a provision of the 2003 law that blocked the government from price negotiations. That's left to the private insurance companies that administer the Medicare drug program.

Independent analysts such as the Congressional Budget Office say the government likely would have little impact on drug prices, since the proposed legislation would not allow it to restrict what drugs Medicare offers. It is that power over so-called drug formularies that enables the government to control prices for veterans.

Still, "the drug companies are going absolutely crazy trying to stop this from happening," said Fred Griesbach, AARP's director of advocacy management.

Ken Johnson, senior vice president of the Pharmaceutical Research and Manufacturers of America, said the coalition of drug companies has been advertising in print and on television "consistently" for months. Both sides are spending millions on the advertising campaigns.

The program can be better, Johnson said, but not through government-dictated prices.

The Bush administration opposes giving the government negotiating authority over prices. Because of that, the House and Senate likely would need two-thirds majorities to override a veto. The House passed the measure by a 255-170 vote, well short of the 290 that would be needed to override.

In the Senate, Democrats will need 60 votes just to allow a vote on the bill. Sen. Ron Wyden, D-Ore., counts about 58 supporters now. The AARP ads are designed to influence undecided senators, mostly Republicans. "It just defies common sense to not have the authority to negotiate," Wyden said.