Car shoppers in a healthy economy, lured by sophisticated incentive programs, are likely to keep on buying at the higher-than-expected rates of the first half of the year, industry analysts say.

The big three domestic automakers last week reported a jump in their sales rates during the June 21-30 sales period.Combined domestic car and light truck sales totaled 459,918 during the late-June period this year, against 359,784 in the same period last year, a jump of 13.6 percent in the daily sales rate.

Combined domestic car and light truck sales totaled 1,120,962 for all of June, an 8.5 percent increase in daily sales, and 6,184,576 for the year through June 30, up 11 percent from the first half of 1987.

"We see sales for the rest of the year as pretty good, with a possible soft spot in October," said Thomas O'Grady, an analyst with Integrated Automotive Resources Inc. in Wayne, Pa.

A late-year lull might occur as buyers wait to see what incentives will be offered on newly introduced 1989 models in dealers' showrooms, he said.

Among imports, car and light truck sales totaled 333,066 for the month, down 7.6 percent, and 1,874,004 for the first half, down 1.5 percent.

For the June 21-30 sales period, Ford Motor Co. sold 89,927 cars, a 27.4 percent jump in daily sales. For the year through June 30, Ford sold 1,161,574 cars, a 12.8 percent increase over the first half of 1987.

General Motors sold 144,205 cars in late June, an 18 percent jump, and 1,952,402 for the first six months, a 4.9 percent increase.

Chrysler Corp. sold 40,817 cars in late June, up 8.4 percent a day, and 574,609 for the first half of 1988, up 14.3 percent.

O'Grady said sales were helped by the apparent success of new models at some automakers, such as General Motors GM-10 models. He also said sales were helped by U.S. automakers' increasing adeptness at offering incentives, with shorter programs and more frequent changes in affected models, smoothing sales peaks and valleys the programs once triggered.

Honda sold 30,049 domestically made cars and 33,279 imports in June, up from 25,015 U.S. made cars and 31,078 imports last June. Toyota sales of U.S.-produced cars for the month reached 3,066, up from 1,228, and its imports rose to 54,906 from 47,584 last June.

Nissan sold 49,957 U.S. produced cars in the first half of the year, down 23.4 percent, and 24,644 imported cars, down 67.3 percent.