A federal judge in Philadelphia yesterday refused to toss away a 12-year-old Ghanaian boy's hope to remain in this country.

U.S. District Judge Franklin S. Van Antwerpen refused a request by the U.S. Immigration and Naturalization Service to throw out a lawsuit that challenges the government's efforts to send the boy back to Africa.

The boy has been in the custody of immigration officials since he arrived at a New York airport nearly 20 months ago - alone, without any travel documents, with only $1.25 in his pockets - on a flight from Ghana.

The boy, who was 10 when he entered the country illegally, contends that a man who identified himself as a friend of his father put him on the New York-bound flight and told him to say, if asked, that his father was traveling with him.

Originally placed by INS at the Georgia Baptist Children's Home in Atlanta for several months, the boy later spent about a year at the Berks County Youth Center, in Leesport, Pa.

He is now living with a foster family in Philadelphia, awaiting the outcome of the court case, a lawyer said.

The Daily News is not publishing the boy's name lest publicity disrupt his adjustment to his foster family or jeopardize his safety.

Immigration authorities contend that no court has authority to review their decision to deport the boy.

But in an opinion and order filed yesterday, Judge Van Antwerpen disagreed.

The boy is represented by two Philadelphia lawyers, Stephen G. Harvey and Gerard A. Dever, of the Pepper Hamilton firm, and by Metty Vithayathil, of the Pennsylvania Immigration Resource Center, in York, Pa.

In court papers, they say the boy is intelligent and in overall good health, but stutters and has nervous tics in his right arm, neck and both eyes, caused by beatings "and/or" being sent alone on a plane to the United States.

He "fears returning to Ghana and insists that he would rather live in INS detention than return to Ghana, even if it means never seeing his father or brother again," the lawyers told the judge in the suit filed in July.

The boy says his dad beat him a lot, "with a belt or the branch of a tree," for coming home late.

The boy also fears killers who he said run rampant in his native land.

The lawyers had the boy examined by Dr. Marc A. Forman, of Rushland, Bucks County, "a highly qualified child psychiatrist" and emeritus professor at Tulane University Medical Center in New Orleans.

The psychiatrist concluded that the boy suffers from post-traumatic stress syndrome, with symptoms including anxiety, sleep disturbances, bed wetting and "depressed effect."

The psychiatrist recommends that the boy not be sent back to Africa.

The boy's father and mother are separated.

While the boy's father told the INS last year that he wanted the boy back, he has recently told the boy's lawyers in a signed declaration and a letter that he didn't want his son to return to Ghana.