WASHINGTON — The government may be paying incorrect subsidies to more than 1 million Americans for their health plans in the new federal insurance marketplace and has been unable so far to fix the errors, according to internal documents and three people familiar with the situation.

The problem means that potentially hundreds of thousands of people are receiving bigger or smaller subsidies than they deserve. They are part of a large group of Americans who listed incomes on their insurance applications that differ significantly – either too low or too high – from those on file with the Internal Revenue Service, documents show.

The government has identified these discrepancies but is stuck at the moment. Under federal rules, consumers are notified if there is a problem with their application and asked to upload or mail in pay stubs or other proof of their income. Only a fraction have done so, according to the documents. And, even when they have, the federal computer system at the heart of insurance marketplace cannot match this proof with the application because that capability has yet to be built, according to the three individuals.

So piles of unprocessed “proof” documents are sitting in a federal contractor’s Kentucky office, and the government continues to pay insurance subsidies that may be too generous or too meager. Administration officials do not yet know what proportion are overpayments or underpayments. Under current rules, people receiving unwarranted subsidies will be required to return the excess next year.

The inability to make certain the government is paying correct subsidies is a legacy of computer troubles that crippled last fall’s launch of HealthCare.gov and the initial months of the first sign-up period for insurance under the Affordable Care Act. Federal officials and contractors raced to correct most of the technical problems hindering consumers’ ability to choose a health plan. But behind the scenes, important aspects of the website remain defective – or simply unfinished.

White House officials recently have begun to focus on the magnitude of income discrepancies. Beyond their concerns regarding overpayments, members of the Obama administration are sensitive because they promised congressional Republicans during budget negotiations last year that a thorough income-verification system would be in place.

Under White House pressure, federal health officials and the contractor, Serco, are this weekend beginning to step up efforts at resolving a variety of inconsistencies that have appeared in applications, including income discrepancies. One White House official, speaking on the condition of anonymity about internal discussions, said that White House and federal health officials are “all on the same page that the issue needs to be resolved as soon as possible.”