For the first time, American home buyers are making average monthly mortgage payments of more than $1,000 for new homes, according to a survey of mortgages made during 1987. The study, done by one of the nation's largest mortgage banking firms, shows not only that home prices are rising, but also that many people are buying more expensive homes, housing experts say.

Lomas & Nettleton Co. said in its U.S. Housing Markets newsletter that the average monthly payment for new homes, including taxes and insurance, jumped 8 percent from $984 in 1986 to $1,063 last year. The higher monthly payment is primarily because of the increase in the average price of a new home financed with a conventional fixed-rate mortgage, which rose 14.2 percent last year from $119,100 in 1986 to $136,000.

In the Washington area, the average monthly payment on a new home jumped from $1,336.24 in 1986 to $1,413.98 last year, among the highest figures in the country. For existing homes, monthly mortgage payments in the Washington area actually fell last year, from $1,309.65 to $1,257.31. The survey also showed that in the Washington area, the average price of a new home last year was $175,300, up from $159,200 in 1986, while the average price of an existing home was unchanged at $155,900.

Even though a new house may be more expensive than it was a year ago, many home buyers are opting for bigger price tags and larger monthly payments because lower interest rates mean more of the mortgage payment is going toward reducing the principal instead of paying interest.

"The tendency is for home buyers to buy more house with the lower interest rate," said James W. Wooten, chairman of Lomas & Nettleton. "They're trying to get all the house they can get."

Many builders said they are constructing homes for the "move-up" or "trade-up" market, catering to the needs of buyers seeking to move into their second or third home, which in most cases means more space and more luxury. Wooten and other housing experts said the costs of these added amenities, along with rising land values and construction costs, are contributing to the steady increase in new home prices throughout the country.

Other cities with high monthly mortgage payments for new homes included Boston ($1,549.40), the New York City area ($1,467.33), San Diego ($1,257.48) and Los Angeles ($1,221.32).

The most affordable cities for housing are in the Midwest, where the monthly payments for new homes were well below the national average in 1987, the survey said. St. Louis ($768.17), the Cleveland area ($938.37), Indianapolis ($976.09), Kansas City ($985.97) and Miami-Ft. Lauderdale ($797.94), were among the cities with the lowest average monthly payments.

With the lower interest rates, many home buyers are making smaller mortgage payments than buyers did five years ago. In 1983, the average cost of a new home in the Washington area was $148,200, but mortgage interest rates were as much as eight percentage points higher than they are now, and homeowners were paying an average of $1,516.32 a month.

"Washington stands to be one of the more stable regions in the country," Wooten said. "It has healthy employment throughout the area and wages have helped people pay a little more for their house."

The survey reinforces the fact that areas such as Washington, Boston, New York, San Francisco and San Diego will always be prohibitive for first-time buyers unless they opt to live substantial distances from the center of town, according to John Tuccillo, chief economist for the National Association of Realtors.

"Under current conditions, a family with an annual income of $20,000 who wants to buy a house would probably qualify for about a $55,000 mortgage," he said.

"If they can put down a 20 percent down payment, that means they could get a $65,000 to $70,000 house. If you look around Washington or even some places on the East and West Coast, you have to admit the first-time buyer is going to be a lot better off buying in Grand Rapids, Mich., or Louisville, where houses are half the price they are here. So the question of affordability is always going to be there," Tuccillo said.

Larry Doff, president of Real-Pro, an Annandale real estate agency, said the Lomas & Nettleton study confirms many of the trends occurring in the Washington area.

"Despite the tremendous appreciation of house prices in this area, the reduction in interest rates has helped offset some of the increase in house price," he said. "Affordability was not a major factor in this market last year and won't be a factor this year. Those with the wherewithal are always going to buy."

As an example of how much people can afford, Doff pointed to a couple he is familiar with that had been paying $650 a month in rent. They had a combined income of $63,000, made a down payment of $13,000 on a house and are taking on a $1,300-a-month mortgage payment.

The survey showed that existing home prices are not rising as much as those for new houses. The average price of an existing home purchased with a conventional mortgage was $117,700 in 1987, up from $107,700 in 1986, the survey said. The average monthly payment increased from $893.80 in 1986 to $918.41 last year.

In the Washington area, the leveling off of existing home prices is a big change from the 27 percent price increase from $119,600 in 1983 to $152,200 in 1985.

Tuccillo said he expects that more buyers may consider looking at existing homes.

"In 1988, new home buyers are going to be spooked for whatever reason -- whether it's the stock market crash or fears of slower economic growth," he said. "We're going to see many people who were going up the price ladder last year come down this year."