For the fifth consecutive year, Utah's birthrate has declined dramatically. However, it's still 13.3 percent above the national rate.

According to a report released Saturday by the Utah Department of Health, Utah's 1987 birthrate - 21 per 1,000 population - was the lowest ever recorded. It was down 28 percent from the 1979 rate of 29 per 1,000.One explanation for Utah's decline is that many families are delaying or deciding not to have children, said John Brockert, director of the Bureau of Vital Records and Health Statistics.

"But we cannot measure the extent of this factor until we have followed this group through their entire 30 reproductive years," he said. "We do know that first births are occurring more frequently among women older than 30 years of age."

Dr. Fred White, director of planning, evaluation and research for the Division of Family Health Services, said more women working outside the home and a decline in spendable income are the key reasons for delaying or choosing not to have children.

"Women nationwide and in Utah are having careers, and raising children is very expensive. Even when couples decide to have children, they have fewer of them."

The bureau produces the annual "Vital Statistics" report from various certificates registered throughout the year. The report tabulates 1987 births (35,285); deaths (9,055); marriages (16,745); divorces (8,985); and estimates Utah's population at 1,678,000 as of July 1, 1987.

An unexpected finding in the 1987 report is that infant mortality was up by almost 4 percent to 8.8 deaths per 1,000 live births among those under 1 year of age. There were 312 such deaths in 1987, only two more than in 1986. But the overall decline in the number of live births resulted in the increased infant mortality rate.

The increased death rate occurred primarily after the first month of life, the report showed. There was a 31 percent rise in the post-neonatal mortality rate (deaths per 1,000 population that occur between the 28th and 364th days of life), and a 16 percent decrease in deaths occurring during the first 27 days of life.