DETROIT (AP) _ A judge has rejected a claim from a woman who said she was the long-lost Siamese twin of an heiress to automobile magnate John F. Dodge, and sought part of his $40 million fortune.

Wayne County Probate Judge J. Robert Gragg ruled Friday that Frances Mealbach, 70, was too late to lay claim to the estate, which was divided under a 1980 probate court order that was upheld by the state Supreme Court.

Mrs. Mealbach, who discovered in 1967 that she was adopted as a child, cited scars on her neck and head as evidence that she was surgically separated soon after birth from Frances Dodge Van Lennep, Dodge's daughter who died in 1971.

Gragg declined to rule on whether Mrs. Mealbach could have been Dodge's daughter, saying what mattered was the amount of time that has elapsed since the estate was settled.

''By permitting (Mrs. Mealbach) to come into the Probate Court four years after all litigation ... has ceased, regardless of how meritorious her claim may be, would contravene the intent of the Michigan Supreme Court, which is to permit final orders to stand,'' Gragg said in his ruling.

''It's not a surprise,'' said Mrs. Mealbach, of Dearborn. ''It's about what I expected.''

Her attorney, James Cunningham, said no decision had been made on whether to appeal Gragg's ruling.

Mrs. Mealbach claimed she learned of her probable relationship with Dodge in 1982, when her daughter showed her a copy of ''The Dodges,'' a book that contained photos of the family.

She said she ''got chills because I did think I looked just like him.''

Dodge died in 1920 and put his estate in a trust that paid interest to his six children, the last of whom died in 1980. The estate was then divided among the remaining heirs. Lawyers estimated that had she been counted among those heirs, Mrs. Mealbach stood to gain about $4 million.

Brothers John and Horace Dodge began turning out cars under their name in 1914. By 1920, their cars were second in sales only to those of the Ford Motor Co.

Their company was bought out for $128 million in 1928 by Walter P. Chrysler, who merged it with his own and kept the name alive.