Many of the loans the F.H.A. insured in 2007 and last year are now turning delinquent, agency officials acknowledge. The loans made in those two years are performing “far worse” than newer loans, dragging down the whole portfolio, Mr. Stevens of the F.H.A. said in an interview.

The number of F.H.A. mortgage holders in default is 410,916, up 76 percent from a year ago, when 232,864 were in default, according to agency data.

Despite the agency’s attempt to outrun its fate by insuring ever-larger amounts of new loans to such borrowers as Ms. Shimon — the current rate is over a billion dollars a day — 7.77 percent of the portfolio is in default, up from 5.6 percent a year ago.

Barney Frank, the Massachusetts Democrat who is chairman of the House Financial Services Committee, said in an interview that the defaults were, in essence, worth it.

“I don’t think it’s a bad thing that the bad loans occurred,” he said. “It was an effort to keep prices from falling too fast. That’s a policy.”

The troubled loans are nevertheless weighing on the agency’s capital reserve fund, which has fallen to below its Congressionally mandated minimum of 2 percent, from over 6 percent two years ago.

The optimism expressed by Mr. Stevens, the F.H.A. commissioner, places him at odds not only with some outside experts but with Kenneth Donohue, the inspector general of the Housing and Urban Development Department, who is also F.H.A.’s watchdog. Mr. Donohue said the drop in reserves was “a flashing red light” that the agency was not taking seriously enough.

“It might be we’ll get ourselves out of this and that everything will be fine, but I don’t paint that rosy a picture,” Mr. Donohue said. “They’re banking on the fact that the economy will continue to improve, that the housing market will begin to sustain itself.”

The most troubling part of all of this is what is backing the FHA loans.