Can jumbos join the party?

If it's not one thing, it's another in the housing market these days.

The average rate on a traditional fixed 30-year mortgage is at its lowest level in more than three decades. But if you need a larger home loan, you may be out of luck.

Most jumbo loans — those valued at more than $417,000 — aren't moving anywhere because, unlike traditional mortgages, Uncle Sam isn't buying or backing them.

That's one big reason behind the large difference, known as the spread, between rates on jumbos and the traditional 30-year fixed.

The cap on "conforming" jumbo loans, those backed by Fannie Mae and Freddie Mac, was lifted this year in certain pricey markets like the Puget Sound area and parts of California and New York. On Dec. 31, it will be reduced, making jumbos even harder to get.

But lately there has been reason to hope for those looking to originate or refinance a hefty home loan. The average rate has been edging lower, falling below 7 percent from nearly 8 in October. Keith Gumbinger, vice president of HSH Associates, says the recent rush to refinance traditional mortgages is creating more liquidity in the overall market.

He expects the market to loosen up further as the Federal Reserve buys billions in mortgage-backed securities.

"What could help in a big way is if the Fed started to buy them up," says Greg McBride, senior financial analyst at Bankrate.com. "If the Fed became (the market), the rates would quickly close the gap to their smaller conforming cousins."