By Caroline Humer

(Reuters) - Americans will pay an average premium of $328 monthly for a mid-tier health insurance plan when the Obamacare health exchanges open for enrollment next week, and most will qualify for government subsidies to lower that price, the federal government said on Wednesday.

The figure, based on data for approved insurance plans in 48 states, is the broadest national estimate for the cost of coverage when President Barack Obama's healthcare reform law takes full effect next year. The prices of the new plans are at the heart of a political debate over whether they will be affordable enough to attract millions of uninsured Americans when enrollment begins on October 1.

Obama, who is facing a Republican threat to eliminate funding for the law or shut down the federal government next week, said the fierce opposition stems from the fear that Americans will embrace the program.

"Essentially they're saying people will like this thing too much, and then it will be really hard to roll back," Obama said on Tuesday in a conversation about healthcare with former President Bill Clinton. "What we're saying is, just look for yourself. Take a look at it, and you will discover that this is a good deal for you."

The Obama administration is counting on signing up 7 million Americans, including 2.7 million younger and healthier consumers who are needed to offset the costs of sicker members, in the first full year of reform through the state exchanges.

A major factor in determining the price was the level of competition among insurance companies, with rates significantly higher in states with fewer players, the U.S. Department of Health and Human Services said in its report.

The new health plans are organized in five tiers with different monthly premiums and out-of-pocket costs: catastrophic coverage, bronze, silver, gold and, in some areas, platinum.

The national average cited by HHS refers to the second-cheapest among silver plans on the market - which many healthcare economists expect to be the most popular for their balance of coverage and out-of-pocket costs. On average, the least expensive plans in this group were reported in Minnesota, where it costs $192 per month, and Tennessee, $245.

Story continues

At the high end of pricing are states with large rural populations, where it can be more expensive to deliver healthcare: Mississippi at $448 per month; Alaska, $474; and Wyoming, $516. Florida came in right at the national average at $328.

U.S. Senate Republican Leader Mitch McConnell said the new plan prices were still a costlier proposition for Americans, based on what they may have paid for individual plans in the past. Under the Affordable Care Act, insurance plans must cover a wider range of preventive and other medical services and cannot turn away applicants based on prior illnesses.

"Even the Administration is having a terrible time spinning this law," McConnell said in a statement. "About the best they could claim was that some premiums would be lower than projected. Note that I didn't say lower, but lower than projected."

HOW AFFORDABLE?

Debate over whether Obamacare will prove affordable for millions of uninsured Americans has intensified in the past few months, as states have announced rates. States that have supported the law said it would lead to lower prices. Others that have opposed the reform - including Georgia, Florida, and Indiana - warned of "rate shock" for consumers compared with what they could buy on the individual insurance market a year ago.

HHS said the average price was 16 percent lower than its own projections on premiums. In addition, consumers who earn up to 400 percent of the federal poverty level, or $62,040 for a couple, will qualify for subsidies that will lower the price further.

The data is mostly based on 36 states where the federal government will operate the insurance exchange. About 14 other states and the District of Columbia are running their own exchanges. Three states - Hawaii, Kentucky and Massachusetts - had not released premium information at the time of the report.

States with the lowest average premium tend to have more insurance companies offering plans, the report said. It said eight issuers on average were selling plans in the states with average premiums in the lowest 25 percent, while states with average premiums in the top 25 percent had only three insurers on average.

Pricing varies widely not only by state but by community. For instance, Florida has 67 different geographical rating areas, and their prices for the second-lowest-cost silver plan range for a 40-year-old from $239 to $352 a month.

"The take-up of the exchanges is going to vary significantly by state and by community as word gets out," said Michael Sparer, professor of health policy at Columbia University's Mailman School of Public Health.

Texas has been among the Republican-led states most fiercely opposed to Obamacare, but its monthly rates came in below the national average, HHS said. With 76 plans to choose from in Austin, a 27-year-old would pay $169 per month for the lowest-cost mid-tier one. In Dallas-Fort Worth, that monthly premium was $217, from 43 plans available, the report said.

"The rates in Texas are looking good," said Gary Cohen, who is charged with overseeing the exchanges at the Centers for Medicare and Medicaid Services.

Insurance industry surveys show rates are the most important factor in drawing consumers to the exchanges, which is key to making the healthcare overhaul work.

Another concern has been that insurance companies will limit access to doctors to keep prices low. Cohen said that these so-called "narrow networks" were a trend before the Affordable Care Act took effect.

The law was adopted in 2010, but two of its main pillars, the health exchanges and the expansion of Medicaid, take effect in 2014. Household names like UnitedHealth Group Inc, Aetna Inc, WellPoint Inc and Humana Inc will sell plans on at least some exchanges. Newcomers such as Medicaid specialist Molina Healthcare Inc will also play a role.

(Additional reporting by Lewis Krauskopf in New York and David Morgan in Washington D.C.; Editing by Michele Gershberg, Lisa Shumaker and Lisa Von Ahn)