Fannie Mae, the largest buyer of U.S. home loans, said its mortgage portfolio grew in April after it reduced the March rate of serious delinquencies on single-family loans it guarantees.

The delinquency rate fell as the company continued to repurchase loans that were at least 120 days late. These buyouts in turn inflated its mortgage holdings for the second month.

Fannie Mae said the unpaid principal balance of its gross mortgage portfolio leaped by an annual 46.4 percent in April to $789.5 billion, after spiking by more than 87 percent in March.

For the year, the holdings are up 6.7 percent after shrinking 1.9 percent in 2009.

The rate of serious delinquencies for single-family loans fell 12 basis points in March, the latest data available, to 5.47 percent.

Fannie Mae said it repurchased about $46 billion in loans from its mortgage-backed securities trusts in April that will not be reflected as liquidated from MBS until May.

Excluding buyouts, the total book of business would have dropped by 4.2 percent in April. Including them, there was a 1.9 percent decline to $3.258 trillion.

Fannie Mae and its counterpart Freddie Mac are buying back tens of billions of dollars in troubled home loans that back their securities. The loans that are being repurchased are at least 120 days late and a capital drain.

The two government-controlled companies, which now have open credit access from the Treasury through 2012, have already drawn about $145 billion combined in federal aid.

Fannie Mae, meantime, said the serious delinquency rate on the multi-family loans it guarantees rose 6 basis points in March to 0.79 percent.

On Tuesday, Freddie Mac also reported portfolio growth and mixed delinquency rates.