Mortgage rates have been responding to the economic tides, which, like ocean tides, rise and fall within a narrow range. Inflation is up just a little (but Greenspan isn't worried about it yet). Housing starts and housing permits are down (but the construction industry isn't worried). Unemployment claims are down but the four-week moving average of unemployment claims is up. American factories are producing more, and American consumers are buying even more foreign-made goods, increasing the trade deficit. 

when the Fed decided a month ago not to raise short-term interest rates, it issued a statement that said the economy is expanding "at a significant pace," but that the degree of strengthening is uncertain.

You can say that again. In fact, Alan Greenspan, chairman of the Federal Reserve, did. At the beginning of his remarks Wednesday to a joint congressional economic committee, Greenspan said: "Little, if anything, has happened since the (Federal Open Market Committee) meeting to alter that assessment."

Later he said the Fed "should have ample opportunity" to raise rates "once sustained, solid, economic expansion is in view."

This is unusually direct language from Greenspan. Usually observers pick apart his words to divine whether he is inclined to raise or cut interest rates or leave them alone. His remarks to the joint committee appear to be a clear sign that the Fed will leave short-term rates alone when it meets May 7.

In keeping with Greenspan's assessment, mortgage rates have stayed about the same, too. The benchmark 30-year fixed-rate mortgage fell 5 basis points to 6.96 percent, according to the Bankrate.com national survey of large lenders. A basis point is one-hundredth of 1 percentage point. The mortgages in this week's survey had an average total of 0.60 discount and origination points.

Greenspan says economic demand is strengthening, "but the dimensions of the pickup are still not clear."

One thing is clear, though: Interest rates will rise this year. No one doubts that. Frank Nothaft, Freddie Mac's chief economist, predicts that 30-year mortgage rates will average 7.1 percent this year. He believes rates will stay within a range of 6.95 percent and 7.05 percent through spring, then rise.

What do you do if he's right, and you plan to buy a house this summer or autumn while paying today's interest rates?

You can get a long-term rate lock if your house is under construction or you know you'll move several months from now. Most lenders will lock a rate for 90 or 180 days. Some lenders will commit to a rate for an even longer period on combined construction-mortgage loans.

Longer rate lock terms usually cost more. With locks greater than 45 or 60 days, the borrower often pays a fee at the time the rate is locked and points when the loan closes.

That's how long rate locks work with Nva-Mortgage.com, for example. Owner Bob Gammache offers extended rate locks up to 180 days. The borrower pays a half-point to lock in the rate -- $500 on a $100,000 loan. On closing day, up to six months later, the borrower pays 0.875 percent in discount points -- $875 on a $100,000 loan.

Paying $1,375 to lock in a rate for six months on a $100,000 loan might be a steep price when rates are steady or going down, but it could be a real bargain if rates rise a lot.

Gammache is telling most clients not to lock right now. He forecasts stable mortgage rates and possibly declines in mortgage rates this summer because corporate earnings are weak and the Fed isn't expected to change rates in May.