The economy continued to improve in June, although growth was not as fast as in earlier spring, according to a monthly survey of purchasing agents at major companies.

The top buying officials continued to say that their biggest problem is inflation, but they reported that the rate of price increased moderated for the third consecutive month.

While the number of officials reporting higher prices remained the same as in May - 57 per cent of those surveyed - the numbers reporting lower prices rose.

According to the survey by the National Association of Purchasing Management, Inc., "Clearly those stuck with higher quotes are a large majority . . . Nevertheless, the spurt in price-cutting is refreshing even if probably temporary. At least it's the largest one-month growth in those reporting price decline in almost 15 years."

Administration economists and many private forecasters think that the economy will not grow as fast in the last six months of the year as it did during the first half. That means that the unemployment picture will not improve as much as it did between January and June.

But most experts think that the sharp spurt in inflation evident in the early months of 1977, will moderate later in the year, although the rate will remain high by historical standards.

E. F. Andrews, who heads the purchasing agents survey, said that the slightly slower economic pace earlier in the spring "was boosted to some degree by recovery from the cold and drought of earlier months."

He also noted that because "the long hoped for pick up in new capital spending (to expand production capacity) is still around the corner," some of those surveyed "see visions of future shortages."

Purchasing agents, who are close to economic developments and often accurately predict changes in the business climate, also said that the employment situation remains strong and that there are few shortages of supplies now.