UPDATE 1-No increase in Medicare drug costs for U.S. seniors

WASHINGTON Aug 6 (Reuters) - Medicare participants enrolled in the U.S. health insurance program's prescription drug benefit should see their premium cost remain steady next year, health officials said.

The Department of Health and Human Service on Monday forecast a $30 average monthly premium for Medicare Part D, similar to the cost in 2012. In 2011, premiums were $30.76.

HHS attributed the low premiums to President Barack Obama's healthcare reform law, known as the Affordable Care Act, which includes some measures to lower the cost of medications for seniors. Last year, HHS also attributed the low premiums to increased competition and greater use of cheaper generic drugs.

The administration has focused on promoting the healthcare law ahead of the November presidential election, which some view as a referendum on Obama's signature domestic policy program.

The voluntary Part D benefit pays for medicines for seniors and disabled Medicare patients who have signed up for separate drug insurance plans through private insurers such as Aetna Inc and Humana Inc.

The government subsidizes the gap between the premium patients pay and the amount that insurers bid to the program.

The healthcare reform law aims to close the Medicare Part D "doughnut hole," or the gap in drug coverage for seniors that starts if total annual spending exceeds a certain level.

The ACA aims to fully close the gap by 2020, and seniors in the doughnut hole have already saved $3.9 billion because of the law, HHS said.