Early this summer it looked as if mortgage rates had hit bottom. After all, a rate of just over 6 percent on the standard 30-year fixed-rate mortgage was a three-decade low.

But as proof that anything can happen, rates have now gone even lower - to a four-decade low.

Yesterday, the Mortgage Bankers Association of America reported the 30-year rate had fallen to an average of 5.99 percent from 6.16 percent a week earlier. This is around the 1963 level, the association said.

The 15-year fixed-rate loan fell to 5.4 percent, a record. And the starting rate on one-year adjustable mortgages fell to 4.16 percent (which is not a record).

About 71 percent of recent mortgage applications involve refinancing of older mortgages.

If you are thinking of refinancing an older loan, or of taking out a new mortgage to buy a home, here are a few things to consider:

Don't delay. Sure, rates could go down more. Fear is driving many investors to flee stocks and buy bonds. The heightened demand drives down the interest rate paid by bonds, and mortgage rates usually follow.

But it would be a shame if holding out for another fraction of a percentage point caused you to miss today's low mortgage rates.

For a reality check, look at dollars rather than percentages. If the 30-year loan rate fell from 5.99 percent to 5.75 percent, the monthly payment on every $1,000 borrowed would fall from $5.99 to $5.84. That's $30 a month on a $200,000 loan - not enough of a saving to justify the risk that waiting could leave you with a higher rate rather than a lower one. After all, it wouldn't take much of a change in market conditions for rates to rise to 6.5, 7 or 7.5 percent.

Go with a fixed-rate mortgage. Today's 30- and 15-year fixed-rate deals are definitely more attractive over the long term than the adjustable-rate offerings.

The reason is that the standard adjustable mortgage payment is recalculated every year based on the remaining debt, the number of years left on the loan - and the new interest rate. Most of these deals specify that the new rate can be no more than 2 percentage points higher or lower than the previous year's rate. Over the life of the loan, the rate adjustments can be as much as 6 percentage points above or below the starting rate.

So if you got a one-year ARM charging today's 4.16 percent for the first year, it could rise to as high as 6.16 percent next year and possibly 10.16 percent someday. A higher rate later could quickly wipe out the savings you'd realize from the low first-year "teaser" rate. Right now, the risk of that is not sufficiently offset by the prospect of the rate falling.

Most one-year ARMs are reset every 12 months by tacking 2.75 percentage points onto the rate paid by one-year Treasury bills. Currently, those are paying about 1.8 percent. So an ARM adjusting now could go to 4.55 percent, unless the cap limiting annual changes to 2 percentage points kept it higher.

While 4.55 percent is obviously lower than the 5.99 percent charged by new 30-year fixed mortgages, there's not much chance one-year Treasuries will stay this low for years.

Because of the 2.75 percent margin, anytime the one-year Treasury is paying more than 3.24 percent, ARMs will adjust to rates above the 5.99 percent you can get today on a fixed-rate mortgage. The fact is, the one-year Treasury rarely pays less than 3.24 percent.

Don't get greedy. Refinancing to reduce your monthly payments is a great move, if you'll have the mortgage long enough for the savings to offset the application fee, title insurance and other costs of refinancing.

But many homeowners are using refinancings to get at money tied up in their homes - by taking out a new loan that's larger than debt remaining on the old one. It's tempting to borrow at today's low rates. Just keep in mind that you could be saddled with the debt for decades. Even with today's low rates, total interest costs can be enormous on loans that aren't repaid for 10, 20 or 30 years.