OMAHA, Neb. — Figures from a survey of supply managers in nine Midwest and Plains states have risen for the third month in a row, according to a report released Friday, suggesting more improvement in the regional economy.

The Mid-American Business Conditions Index rose to 50.6 in March, compared with 50.5 in February and 48.3 in January, the report said. The December figure was 39.6.

But the strong U.S. dollar and weakness among the nation’s major trading partners are continuing to restrain regional growth, said Creighton University economist Ernie Goss, who oversees the survey.

“The strong U.S. dollar not only undermines exports, it also reduces the value of foreign earnings,” Goss said in a news release. “The strong dollar has made U.S. goods much less competitively priced abroad.”

The index for new export orders rose to a growth neutral 50.0 in March from 46.1 in February. The import index rose to 55.4 from February’s 50.1.

In Minnesota, the overall index declined to 50.7 in March from February’s 52.1. Components of the Minnesota index were new orders at 53.5, production or sales at 50.6, delivery lead time at 50.9, inventories at 52.1 and employment at 46.2. “Since the beginning of the recovery in 2009, Minnesota’s manufacturing sector has added almost 17,000 jobs while output per worker has expanded by approximately 10.4 percent,” Goss said. Creighton’s surveys over the past several months point to higher manufacturing output but with the number of manufacturing jobs remaining flat for the next three to six months, he said.

This month the survey included a question about the importance of international market access. More than three-quarters of the supply managers who responded said the access is important for sales to customers in those markets and purchases from companies in those markets.

The survey results are compiled into a collection of indexes ranging from zero to 100. Survey organizers say any score above 50 suggests economic growth. A score below that suggests decline. The survey covers Arkansas, Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, Oklahoma and South Dakota.

Economic optimism, as reflected by the business confidence index, jumped to 51.4 last month from February’s 46.8.

“Improving prices for manufactured products and commodities bolstered positive expectations of future regional economic conditions,” Goss said.

The regional employment gauge remained below growth neutral but increased to 45.9 from February’s 44.4.