A Montgomery County dentist was acquitted yesterday of charges that he kidnapped his wife last year after she had left him and moved into her mother's home with their children.

Dr. Robert Griffith, 44, also was acquitted in Prince George's County Circuit Court on charges of false imprisonment, assault and battery in connection with the alleged kidnaping.

But the jury of eight men and four women found the Derwood, Md., dentist guilty of breaking and entering the Hyattsville home of his mother-in-law on the morning of the alleged kidnaping last June.

While waiting for the verdict, prosecutor Michael P. Whalen predicted the jury would vote acquittal on the kidnapin charge. "The problem," he said "is that juries are very wary of husband-wife cases if they don't involve brutality. They still feel that those things might belong in divorce court."

As Whalen spoke, the jury was reaching its decision on the two-day trial. Emerging after five hours of deliberation, foreman Jay W. Lounsbury said the jury came to the conclusion that "there was reasonable doubt that Mrs. Griffith was unwilling to go along with her husband that day."

Griffith's wife, Judith, testified Wednesday that on the morning of June 27, 1978, she was preparing breakfast for her two young children in the kitchen of her mother's home where they had been living for a month. All three were dressed in their night clothes, she said, when her husband came through the door, grabbed them and announced, "We're going to Mexico."

Griffith 43, testified her husband forced her and the children into a rented car. They got as far as Fredericksburg, Va., she told the jury, and spent the night there in a motel. The next morning she presuaded her husband of 22 years to return home, promising that she would return with him, according to testimony.

Dr. Griffith testified that he had merely hoped t reconcile with his wife and started off for a Mexican vacation with his family to try to patch up the marriage. He refused comment after the verdict.