DALLAS -- In a significant shift, nearly two-thirds of American home builders are now constructing houses for homeowners looking to move into bigger, more expensive homes rather than for first-time buyers.

In a survey of 615 builders taken here at the National Association of Home Builders' annual convention, 65.7 percent said they are building homes for so-called move-up buyers, those who are moving from a first or second home into one with more space or more amenities, or both. A year ago, in a similar survey, 53 percent of the builders said they were building for move-up buyers.

Conversely, 29.4 percent of the builders in the latest survey said they are building cheaper houses for the first-time buyer, down from 43 percent a year ago. A total of 4.9 percent of those polled said they build housing for the elderly, up slightly from last year.

"It's really a direct trade-off," said Kent W. Colton, executive vice president of the home builders' trade group, of the shift away from construction for the lower end of the housing market. "That's where the market is going."

Several studies have shown that as the price of housing has steadily risen in recent years, would-be first-time home buyers have had to delay buying a house or forgo buying altogether.

As of the third quarter of 1987, 64.2 percent of all households in the United States own their homes, down slightly from the peak figure of 65.6 percent reached in 1980, but up a notch from the dip to 63.8 percent two years ago.

What the overall figures mask, however, is that home ownership among younger adults is declining. Home ownership among 25- to 29-year-olds has dropped from a peak of 44 percent in 1979 to 36.9 percent in the third quarter last year, while the figures show a dip from 62.4 percent (in 1976) to 54.5 percent for 30- to 34-year-olds.

In a policy statement approved here, the builders said the young home buyers' plight was in part the fault of the Reagan administration because of its 70 percent reduction in federal housing spending since 1980. But the NAHB also blamed local governments for "imposing excessive fees that in many cases add tens of thousands of dollars to the price of a home and go far beyond the actual costs associated with new development."

Colton said the organization "in a policy sense {is} very concerned about the first-time home buyer" and, among other measures, favors creation of savings incentives in the federal tax code that would encourage would-be young buyers to set aside money for housing down payments.

Asked if the association's membership, by building more homes for the move-up buyer, is at odds with the stated goals of the group's leadership, Colton replied, "They're reacting to the demographics of where the market is going. The membership are building homes where they can sell them. They're concerned about those issues. They're concerned, but they're not dumb. We're telling them to build where they can sell."

Anthony Natelli Sr., president of the Suburban Maryland Building Industry Association and the developer of the expensive Avenel residential and golf course complex in Montgomery County, said the national trend of more construction for move-up buyers is mirrored in the Washington area. The builder survey here showed that the typical builder last year constructed a home that cost $185,200, a figure Natelli said he believes Washington area builders matched or topped. The builders predicted the median price of a new home would rise about 5 percent this year.

With land prices skyrocketing in the Washington area, Natelli said new homes for first-time buyers increasingly will be those offered at the ever-expanding fringe of the metropolitan region.

In other findings the survey showed: Slightly more than half of the builders believe the number of housing starts this year will equal 1987's 1.6 million total, which would be about 100,000 more than most housing industry groups, including the NAHB, are projecting.

Almost half of the builders (48.4 percent) said the stock market plunge last October has had no impact on their businesses, although 40.7 percent said it did.

The decline in mortgage interest rates after the stock market collapse boosted home sales for 37 percent of the poll respondents.