Housing activity is expected to take a severe hit this year from higher interest rates, but one important category could be an exception. Remodeling activity could increase.

In fact, say some housing people, it is conceivable that any difficulty in selling new or used homes might actually spur remodeling activity.That theory is based on the assumptions that homeowners with plans to move to more expensive homes might remodel instead of moving and that new buyers might opt for less expensive fix-up properties.

In short, while remodeling might seem costly it still might be less so than expenses involved in moving household goods, obtaining a new mortgage with points attached and paying legal and other closing costs.

Those factors could explain the high degree of optimism found in a survey of remodelers conducted by the National Association of Home Builders.

Of 2,000 remodelers surveyed, 78 percent said they expected dollar volume to rise this year. And 62 percent of respondents said they expected the dollar increases to total 11 percent or more over 1988, which was a record year.

For the first time in any year, money spent on home remodeling in 1988 exceeded $100 billion, compared with half that in 1983. Uninterrupted increases since 1984 have made it the fastest growing segment of construction.

The survey underscores what many people already know - that kitchens, baths and room additions are the most popular remodeling jobs. Room additions alone accounted for 25.5 percent of activity, with total rehabilitation accounting for 7.9 percent.

The median cost (half above, half below) was $6,700 for a bathroom, $15,000 for a kitchen, $30,000 for a new room, $40,000 for a second-story addition and $44,285 for a complete remodeling job.

The practical use of such figures, however, is limited to establishing a sense of relative values, because the cost of any remodeling job is affected by particular characteristics and even more so by geographical area.

Whatever use the figures are put to, anybody who undertakes a remodeling job should be aware that the initial estimate is not always the final one.

While the remodelers surveyed during the final quarter of 1988 expressed tremendous confidence for 1989, they nevertheless cited several problems. Sixty-six percent griped about low bidding by competitors.

Kenneth Klein, a Tulsa remodeler and chairman of the NAHB Remod-elors Council, contends the industry is plagued by contractors who run a remodeling business out of the back of a truck and are unlicensed and uninsured.

Because they have almost no overhead costs, such contractors often are able to submit the lowest bids. But, says Klein, they also present the consumer with the least assurance that the job will be completed satisfactorily.