NEW YORK (CNNMoney.com) -- Two key proposals to improve access to health insurance could reduce the ranks of the uninsured but cost $1 trillion over 10 years, according to preliminary estimates released Monday by the Congressional Budget Office.

The estimates are the first in a series over the next few months that will attempt to quantify the costs and benefits of various health reform options. President Obama, citing the huge part health care spending plays in the economy, has made passing reform this year a top priority.

The report by CBO, an independent agency that scores legislative proposals for lawmakers, focuses on proposals to create health insurance exchanges and subsidize the cost of insurance for some households.

The agency estimated that the exchange and subsidies could reduce the number of uninsured people by roughly 16 million by 2015. It is estimated there would otherwise be 51 million uninsured that year.

The CBO estimates are based on parts of a health reform bill from Democrats on the Senate's Health, Education, Labor and Pension Committee, chaired by Sen. Ted Kennedy, D-Mass.

The committee will start debating and amending that bill on Wednesday.

Under the bill, the federal government would give grants to states to set up insurance exchanges that consumers could use to comparison shop for health insurance. And it would offer subsidies of varying levels to help families with incomes up to 500% of poverty level (roughly $110,000) to pay for coverage.

The federal government would also subsidize small businesses that offer health benefits but have workers with low wages.

The CBO stressed that its estimates are preliminary for several reasons:

They only reflect analysis of one part of the health committee bill. So they aren't a comprehensive look at the potential costs and savings of all measures in that bill.

They do not reflect the likely interactions that will occur with other elements of comprehensive health reform that may be included -- such as an expansion of Medicaid or the creation of a public insurance plan, which is the most controversial issue in the health reform debate.

In addition, the CBO has not yet finished its analysis of all the bill's elements, such as a proposal to let parents cover their children as dependents until they're 27.

The health committee bill is hardly the last word on health reform. Other congressional committees have jurisdiction over other parts of health care reform.

One is the Senate Finance Committee, which will oversee the tax proposals intended to help pay for the overhaul of the health care system.

The finance panel's chairman, Sen. Max Baucus, D-Mont., is expected to release a draft of his health reform bill this week.