The number of homeowners who defaulted on their mortgages even after securing cheaper terms through the government’s modification program nearly doubled in March, continuing a trend that could undermine the entire program.

Data released Wednesday by the Treasury Department and the Housing and Urban Development Department showed that 2,879 modified loans had been ended since the program’s inception in the fall, up from 1,499 in February and 1,005 in January.

The Treasury Department said it could not explain the growing number of what it called cancellations, almost all of which were apparently prompted by the borrower’s being unable to make the new payment. A scant number — 37 — were because the loan had been paid off, presumably because the borrower sold the house.

About seven million households are behind on their mortgage payments.

The Obama administration’s modification program has been widely criticized for doing little to help them. The program received another bad review on Wednesday with the release of a report from the Congressional Oversight Panel.