As the nation's economic recovery heads into its fourth quarter, all eyes remain fixed on the credit markets. Unfortunately for financial planners, every eye beholds a different prospective path for interest rates.

They're headed down, says Treasury Secretary Donald T. Regan.

Up, says First Boston Corp. economist Albert Wojnilower.

Down, then up, says Michael Sumichrast of the National Association of Home Builders.

Not a lot of change, says Jack Carlson of the National Association of Realtors.

Indeed, some economists have taken to expressing their predictions in percentages, like weather forecasters. William A. Niskanen Jr. of the Council of Economic Advisers sees a 70 percent chance that rates will rise about 1 percentage point and a 30 percent chance they will drop by as much as three points.

"It's hard to say," says F. Peter Gaffey, of the mortgage banking firm of Lomas & Nettleton, in the understatement of the day, "where rates will go from here."

To the extent that there is any consensus to be found among the forecasts, it is that there will be minor, short-term jumps in both directions, whatever the overall trend.

" . . . The market will remain jumpy, twitching at every piece of good or bad news, at least until the Treasury completes the funding, sometime in October, of the fiscal 1983 deficit," says Gaffey.

The outlook is in marked contrast to that of a year ago, when rates were beginning a dramatic slide that was to take the prime rate back into single digits and mortgage rates from the 16 percent range down to the 12- to 13-percent level. In mid-September 1982, the FHA mortgage rate stood at 14 percent; in May it was 11 1/2 percent.

"For a period of about six months, from November to late May, it was possible to tell oneself that stability had returned to the mortgage market," said Gaffey.

But late spring proved to be the bottom of the slide. Today the prime is back above 10 percent, FHA mortgages are up to 13, and conventional mortgages are just under 14.

Now the question that businessmen most want answered--and that economists are unable to answer with certainty--is whether this is the beginning of another period of quickly escalating interest rates.

Wojnilower, widely respected for his forecasts, thinks it is. He said last week he believes financial institutions will bid up rates on deposits, forcing the Treasury to pay more to market its debt. Under the circumstances, he said, he thinks the rise will continue until it is damped by another recession.

Secretary Regan, on the other hand, has said repeatedly in recent days that the Reagan administration's policies are wringing inflation out of the economy and "shrinking inflation . . . works as a force for shrinking interest rates."

Also optimistic is Mark J. Riedy, executive vice president of the Mortgage Bankers Association of America. He foresees a half-point decline in mortgage rates between now and the end of the year, and another half-point drop next year.

Riedy says the "shape of costs across the industrial sector look pretty good," and he believes the federal budget deficit, while "a disaster," has "already been discounted by the market." Inflation has stayed down quite a while now, he adds, and "long-term investors have got to begin believing."

He also notes that next year is an election year, and "the old theory that rates come down in election years . . . has almost never failed . . . . The policymakers have too much invested in a sustainable recovery" to let it be killed off by an interest rate surge.

The Realtors' Carlson says that while rates may decline a half-point over the remainder of this year, he expects conventional mortgage rates to remain in the 13 to 14 percent range. "The pressure will be on the upside next year, not the downside," he says.

Carlson added that the rise during the summer has already damaged the housing recovery, and he expects further slowing this year and next. "We have passed the peak" in both housing starts and resale volume, he said, and he expects 1984 to fall short of '83 in both categories.

However, Carlson said he doesn't expect any dramatic rate surge because he foresees only "modest growth" in the economy generally. He projects annual growth of the gross national product at 2 to 3 percent for 1984, far less than usual for this stage of a recovery.

But "during none of the previous recoveries were we saddled with financing a $200 billion federal deficit," he said.

Homebuilders, facing not only the current higher rates but also the continued uncertainty, have already cut back on construction and are scaling back future plans as well, according to Sumichrast.

He said that a Home Builders' survey of 800 of its members shows "expectations for the next six months very much down." Actual sales for the first week in September were down as well, the survey showed.

He said his group's "basic scenario assumes a rate decline of half a point through the end of the year and maybe a little into next year." He expects the prime rate to remain in the area of 10 1/2 to 10 3/4 percent. But, looking farther out, Sumichrast finds the prospects alarming.

"I'm particularly worried about 1985," he said. "We are getting set for a collision in the financial markets" between the federal deficit and the credit needs of the economy.

"I'm terribly pessimistic . . . ," Sumichrast said. "I can't see us getting out of this unless we raise taxes, and I don't see Congress doing that."