BOSTON (AP) _ A federal appeals court has upheld a lower court ruling that blamed defective design of a Winchester rifle for an accidential firing that injured two New Hampshire teen-agers during a 1977 hunting trip.

The 1st U.S. Circuit Court of Appeals rejected arguments from the manufacturer of the rifle, Olin Corp., that a federal judge in New Hampshire erred when he held the company liable for the shooting.

Damages were not an issue in the appeal, but the victims, Henry Fortier and Raymond Croteau, were awarded a total of $560,000 as part of the Sept. 16, 1986, decision by U.S. District Judge Martin F. Loughlin.

Fortier and Croteau suffered foot wounds when a third teen-ager, Paul Croteau, stumbled and fell during the hunting trip near Berlin, N.H. The rifle discharged when it hit the ground, and the bullet passed through Raymond Croteau's left foot then pierced Fortier's right foot.

''It could reasonably be concluded from the evidence that the defective design made the rifle unreasonably dangerous for the purpose sold - to be used as a hunting weapon,'' the appeals court said in a decision published Thursday.

''There was evidence that defendant, despite its denial, had a consumer product safety committee which was aware that there could be an accidental discharge caused by a hunter falling while carrying a rifle in a position similar to that of Paul Croteau on the day of the accident,'' the court said.

Howard B. Myers, the New Hampshire attorney who represented the Connecticut-based company, did not immediately return telephone calls from The Associated Press on Monday. An Olin spokesman said he did not know if the company would appeal.

At the New Hampshire trial, three firearms experts who testified for the victims blamed the accident on the design of the Winchester Model 94 rifle, a commemorative replica of the original 1866 Winchester. One of them testified that because of its weight, the firing pin was thrust forward when the rifle hit the ground and caused the bullet to discharge even though the gun was half cocked, which acts as a safety on the rifle.

Two of the experts testified that they had tested the rifle and said it would fire, even when in the half-cocked position, if rapped with a hand or a rubber mallet.

The victims also introduced evidence that Olin conducted tests on the rifle in 1974 and 1976 to determine if it would fire when dropped to the ground. The tests indicated that the gun fired a small percentage of the time.

Also introduced as evidence by the victims was a 1976 letter in which an Olin weapons engineer said it would cost between $1.75 and $2.50 a rifle to add an additional safety.

In 1982, U.S. Repeating Arms of New Haven, Conn., which had obtained licensing rights to the Winchester name from Olin, introduced a modified version of the rifle with a lighter weight firing pin. U.S. Repeating Arms since has been purchased by another company.