The percentage of past due loans held by the nation’s largest mortgage financier has fallen.

In its monthly summary report just released, Fannie Mae said the serious delinquency rate on single-family mortgages in its portfolio dropped to 5.47 percent in March, down 12 basis points from 5.59 percent in February.

It’s the first time the GSE’s serious delinquency rate has declined since March 2007, when it was a mere 0.62 percent.

Since that time it’s been a steady upward jaunt, with the pace picking up considerably over the last couple of years. In March 2008, the percentage of Fannie’s loans that were at least 90 days past due was 1.15 percent. By March 2009, it had risen to 3.15 percent, and now 12 months later, it stands at 5.47 percent.

As DSNews.com reported earlier, Fannie’s sibling is also seeing the downside of the delinquency arrow. Freddie Mac’s serious delinquency rate dropped 7 basis points to 4.13 percent in March, also marking its first monthly decline in three years.

Freddie reports delinquency numbers a month ahead of Fannie, and its downward trail is continuing. April marked the second consecutive month that Freddie Mac’s serious delinquency rate has fallen, declining another 7 basis points to 4.06 percent.

Is this the beginning of a trend that will soon spread through the rest of the industry?

Total nonperforming loans in Fannie Mae’s guaranty book of business were $223.9 billion as of March 31, 2010. At that time, the GSE held 109,989 REOs, carrying a total value of $11.4 billion.

Fannie also reported that its monthly transaction numbers include approximately $46 billion in loans purchased from mortgage-backed securities (MBS) trusts in April 2010 that will not be reflected as liquidated from MBS until May 2010.

Excluding these loan repurchases and the impact of March repurchases, the GSE’s total book of business would have declined at an annualized rate of 4.2 percent for April.

Both Fannie and Freddie announced back in February that they would begin buying back 120-plus day delinquent mortgages from securities pools, to minimize the impact of new accounting rules, which require lenders to account for certain securitized assets on their own books.