WASHINGTON, June 15 (Reuters) - U.S. Senator Edward Kennedy's plan to expand U.S. healthcare coverage would increase federal deficit by about $1 trillion over 10 years, the nonpartisan Congressional Budget Office estimated on Monday.

In a letter to Kennedy -- chairman of the Senate's Health, Education, Labor and Pensions Committee -- the CBO estimated that once the plan was fully implemented, about 39 million Americans would get coverage through new insurance exchanges.

At the same time, the CBO said in its preliminary analysis, the number of people who receive coverage through an employer would drop by about 15 million or 10 percent, and coverage from other sources would fall by about eight million. The CBO said "the net decrease in the number of uninsured people would be about 16 million."

There are now an estimated 46 million Americans without any health insurance.

(Reporting by Rick Cowan and Thomas Ferraro, Editing by Sandra Maler)