Midshipman Jeffrey M. Bellistri, expelled from the Naval Academy last month because a random urinalysis showed he had used cocaine, was reinstated today by Navy Secretary John F. Lehman Jr.

Lehman said an investigation by his office, including a polygraph exam administered to Bellistri by the FBI, found "insufficient evidence" to conclude that Bellistri "knowingly used" cocaine.

Bellistri, 23, a senior from Severna Park, Md., and an All-America candidate on Navy's lacrosse team, has consistently denied using the drug since he was tested Nov. 12. The Navy conducted three hearings on Bellistri's case and maintained that its test showed he had 16 times the acceptable level of a cocaine-related substance in his system. Bellistri had been away on leave for several days before the test.

At a hastily called news conference after receiving news of his reinstatement today, Bellistri said he was very happy and holds no grudge against Naval Academy officials. "I hope to make the Navy proud," said Bellistri. "I know the secretary of the Navy won't regret his decision."

Wearing his Navy uniform for the first time since his expulsion in March, Bellistri appeared before reporters flanked by his mother and five brothers and sisters. His only regret, he said, is that his father, who died two and a half weeks ago of lung cancer, did not live to hear the news.

"I wish my father could be here," he said. "He passed away at the end of March. This was his dream, that I graduate from the academy."

Bellistri openly challenged the Navy when he was recommended for expulsion after a series of academy hearings. He called a news conference to protest his innocence and unsuccessfully sought a court order that would have allowed him to attend classes while he appealed his ouster to the Navy secretary.

Academy officials took the unusual step of responding in kind, holding a news conference of their own to defend the drug testing program and their decision to expel him.

Bellistri and his lawyers contended the large-scale testing program was fraught with possibilities for error. They said urine samples could get mixed up or be deliberately tampered with.

Lt. Dave Morris, a spokesman for the Navy at the Pentagon, said today the academy had no plans to alter its testing program.

"We're abiding by the secretary of the Navy's ruling," said Paul Brawley, an academy spokesman. "We will make all the necessary arrangements for Midshipman Bellistri's return."

Lehman said in a prepared statement that he continues to have "the utmost confidence in the Navy's drug testing program." He said there had been only 11 errors in 1.8 million Navy urinalysis tests administered since the program began in 1981. The tests annually result in the dismissal of thousands of Navy men and women.

Brawley said the polygraph test ordered by Lehman was the third taken by Bellistri. Two earlier tests -- one conducted by the academy and one arranged by Bellistri's attorney -- proved inconclusive, Brawley said.

Bellistri said he plans to return to the Naval Academy Monday to meet with his instructors to discuss ways he can make up five weeks of lost class time. He said he's also eager to rejoin the lacrosse team, which has an 8 and 0 record so far this season.

"I want to get back and help 'em out," said Bellistri.

After today's late afternoon news conference, held at the Sly Force Tavern in Crofton, where Bellistri's brother is a chef, the Bellistri family celebrated with a round of beers and prepared to get together with close friends during the evening at their home.

Bellistri's lawyer, David Simison, said the case had been costly for the family, not only in its emotional toll but in legal fees, which total $20,000. He said a legal defense fund is being established.