The latest version of the federal Home Affordable Refinance Program went into full swing this week.

The program, which officially began in December but wasn’t fully available until this week, now allows homeowners to refinance at today’s low interest rates if they are current on payments and hold loans on which they are more than 125% underwater.

The program is limited to homeowners whose loans are backed by Fannie Mae and Freddie Mac. That means no principal will be reduced, but it may be possible to get a lower interest rate and a lower payment. Homeowners who aren’t eligible for HARP may be eligible for other modification programs.

To get a HARP 2.0 refinance, homeowners must have taken out their loan before June 1, 2009. You can read all the guidelines here . The plan will be effect until the end of 2013.

You can apply for a HARP Refinance at E Loans Mortgage.

The previous version of HARP limited the refinancing to homeowners who owed less than 125% of their home’s value.

• The enhanced HARP is one of a number of refinancing and mortgage-modification opportunities unveiled in recent months to keep more homeowners out of foreclosure and in their homes.

Economists believe putting more money into homeowners’ hands, through lower payments also will help the economy.

• As Mark Zandi and Cristian Deritis wrote in an analysis for Moody’s Analytics:

The economic benefit of a restrung HARP is clear. If more mortgages are refinanced, fewer borrowers will default, homeowners will have more to spend elsewhere and the fragile recovery will receive a quick and potentially sizable cash infusion.

If you think you want a HARP refinance, you should move quickly. Mortgage rates have already started rising, so you want to lock in a low rate while you can.