While most Rocky Mountain states face a steady growth or decline in the number of high school students, Utah must cope with a student population roller coaster, a multistate education organization says.

Utah's high schools graduated 20,073 seniors in 1986, the Western Interstate Commission for Higher Education said in its monthly newsletter for May.But the number of high school graduates in Utah is expected to jump to 25,370 by 1992 and balloon to 33,077 in 1998 before tumbling to 29,590 in the year 2004, commission spokesman Charles Lenth said.

While the number of Utah high school graduates will decline by about 3,500 between 1998 and 2004, the state will have a net jump during the next 16 years of about 9,500 students, the study said.

This goes against a national trend, Lenth said, of a "steep slump" in high school graduates in the late 1980s and "then sustained increases into the new century."

State education planners must watch their own student populations and not U.S. averages, he said, "because inappropriate generalizations of national trends could provide worse guidance than no information at all."

Arizona and Nevada both can expect a steady climb in the numbers of high school graduates through 2004, while Colorado and New Mexico will experience slight declines or no change through 1992 and then increases in graduates into the next century.

During the same period, Idaho, Montana and Wyoming should all expect declines in the number of high school graduates, ranging from 14 percent in Montana to as much as 23 percent in Idaho by the year 2004.

The Western Interstate Commission on Higher Education is a non-profit agency serving 13 western states and higher education institutions in those states.