There’s no mystery as to why Congress is not doing more to help the economy: Disagreements between Republicans and Democrats have paralyzed the institution. In February 2011, congressional gridlock almost shut down the federal government. In August 2011, it almost caused a global financial crisis by breaching the debt ceiling. Markets are beginning to worry — rightly — that congressional paralysis might push the economy over the fiscal cliff in January 2013. At this point, the best we can hope for with Congress is that it will manage not to make things much, much worse. Asking lawmakers to make anything better is like asking them to build a rocket to the moon.

But there’s a real mystery as to why the Federal Reserve is not doing more to help the economy. Ben Bernanke, after all, keeps saying the central bank can do more, and if the economy gets worse, it will do more. But the economy keeps getting worse, and the Fed keeps not doing more.

When I say “the economy is getting worse,” I’m using the Fed’s own data. In January 2010, the Fed projected that that the economy would grow 4.15 percent in 2012. By June 2011, it had revised that down to 3.5 percent. By April 2012, it was down to 2.65 percent. And in June, officials lowered expectations once again, saying they expect economic growth to be a mere 2.15 percent in 2012. Ouch.

Some argue that there’s nothing more the Fed can do. But Bernanke is not one of these people. “I wouldn’t accept the proposition, though, that the Fed has no more ammunition,” he said in June. “I do think that our tools, while they are nonstandard, still can create more accommodative financial conditions, can still provide support for the economy, can still help us return to a more normal economic situation.”

So why isn’t the Fed using those tools? Explanations vary. Some believe the Fed doesn’t think it can do much more, and it prefers to hold the few options it has left in reserve in case there’s another major crisis. Others think Bernanke is cowed by Republican pressure and dissent among the Board of Governors. Another explanation — and the one Bernanke has voiced — is that, right now, the Fed believes the risks of doing more outweigh the benefits, but that if the economy worsens, that calculus might change.

I don’t pretend to know what is truly in the heart of our top central banker. But in conversations with Fed watchers and economists, I am convinced that there is something more the Fed can do, and that now is the right time for them to do it. I call it Uncle Ben’s Crazy Housing Sale.

Tomorrow morning, Bernanke could walk in front of a camera and announce that the Federal Reserve intends to begin buying huge numbers of mortgage-backed securities with the simple intention of bringing the interest rate on a 30-year mortgage down to about 2.5 percent and holding it there for one year, and one year only.

The message would be clear: If you have any intention of ever buying a house, the next 12 months is the time to do it. This is Uncle Ben’s Crazy Housing Sale, and you’d be crazy to miss it.

This is a particularly good time for Uncle Ben to launch his sale, because the housing market appears to be turning: More houses are being built, the price of existing homes is beginning to rise, and inventory levels are falling. A recent Wall Street Journal poll of economic forecasters found that 44 percent thought housing had bottomed out, while only 3 percent thought the housing market had further to fall.

The Fed, in other words, would be working with the economic trends rather than against them. People already sense that the housing market is recovering, and that this might be the time to buy — in the unusual, self-perpetuating way of the economy, that’s part of why the housing market is recovering. But with an announcement like this and the attendant media coverage — people would know, with some certainty, that this is the time to buy, and there won’t be a better one for a long time.

This idea comes with high-profile supporters. Joseph Gagnon, a senior fellow at the Peterson Institute for International Economics and a former associate director of the Federal Reserve’s Monetary Affairs Division, has a proposal along these lines. Dan Tarullo and Janet Yellen, both members of the Federal Reserve Board, and Charles Evans, Eric Rosengren, and John Williams, who lead the Federal Reserve’s Chicago, Boston and San Francisco branches, have all suggested that the Fed should buy more mortgage-backed securities. Even Bernanke has called it “a viable option.”

So come on, Ben. Start the sale.