NEW YORK (AP) _ Nearly two-thirds of American companies have no plans to hire or fire workers this spring, a sign that demand for new employees is beginning to level off, according to a survey of second-quarter hiring plans.

The survey, released Friday by temporary staffing agency Manpower Inc., marked the first evidence of a possible slowdown in new hiring by companies across the country.

``We have seen remarkably consistent demand for new workers for more than three years and very substantial hiring remains to be done,'' said Jeffrey Joerres, president and chief executive of Milwaukee-based Manpower. ``But the slowdown now on the horizon is considerably greater than seasonal variation alone.''

The report, based on a survey of 16,000 businesses nationwide, showed that 28 percent will need additional staff in the second quarter, while 8 percent plan cutbacks. Some 59 percent expected their work forces to be unchanged, and 4 percent were uncertain.

A year ago, 32 percent said they would hire staff, while 6 percent predicted cuts. Some 58 percent expected no change and 4 percent were uncertain.

Manpower has conducted quarterly employment surveys for 25 years. The margin of error in the telephone survey, which includes companies in 488 cities, is plus or minus 2 percentage points.