For the first time in years, the housing industry is seeing some positive -- though modest -- signs of an upturn.

Industry experts are not predicting a full-fledged recovery in the depressed housing market any time soon, but they have become more hopeful of a gradual, moderate improvement this fall. This outlook is based largely on predictions that mortgage interest rates will continue edging down--at least for awhile.

Builders particularly have had a change of heart in the past few weeks, showing a higher degree of optimism than they have had for two years, according to new preliminary figures from the National Association of Home Builders.

An NAHB survey of builders' predictions on their own sales in the next six months took a great leap for the better between July and August, the largest monthly change recorded in the 27 years the association has been taking the survey.

The survey also showed that both sales and traffic at projects improved in August to their highest level since April 1981, by no means a banner month but still better than the dismal figures that have persisted this year.

"I don't want to sound terribly optimistic, because I'm not," said NAHB Chief Economist Michael Sumichrast. "Sales are still terrible, just not as terrible."

But Sumichrast also predicted that July will prove to have been the bottom of the nearly-four-year housing depression. "I'm cautiously optimistic that the worst is over for us . . . that we won't slide further down in the mudhole." he said.

He did, however, say that bankruptcies of builders are likely to shoot up in September, as more builders simply will not be able to hold out long enough to take advantage of any improvement.

On actual sales of single-family homes, 87 percent of all builders surveyed in July said sales were poor, only 7 percent said they were fair and 6 percent said they were good to excellent. For August, 75 percent said sales were poor, but 20 percent said they were fair and 5 percent said they were good to excellent.

The improvement in predictions was more dramatic, however. In July, 77 percent said the next six months would be poor, 19 percent fair and 4 percent good to excellent. In August, 46 percent said they expected poor sales, 45 percent fair sales and 9 percent good to excellent.

Both builders and real estate brokers report that, in the past two weeks, more people have returned to at least looking at both new projects and homes being resold, probably prompted by the recent pieces of positive economic news generally.

Whether this increased traffic will translate into more sales contracts is another matter, however, and most industry experts say it is too soon to tell just how significant the renewed activity will prove to be.

If interest rates go on the rise again after only a short decline, this likely would turn any improvement into a false start. And at this point the experts are divided on just where the rates will be going by the end of the year.

Some, like Sumichrast, predict rates will continue to decline, although probably in a zigzag fashion. This would lead to a "reasonably good" 1983 for the industry, he said.

Others, like Mark Riedy, executive vice president of the Mortgage Bankers Association, see rates going down for a few months and then returning to current levels, staunching any significant recovery.

On one thing they all seem to agree, however: The industry still will have a long way to go before becoming healthy again regardless of what happens between now and the end of the year.