Navy Secretary John F. Lehman Jr. has sent Congress a strong defense of the Navy's handling of Vice Adm. Joseph Metcalf III's involvement with Soviet arms captured in Grenada, saying that more than 300 Marines who also tried to bring captured arms home were treated less harshly than the admiral.

Lehman provided the first count of enlisted men who, like Metcalf, tried to bring captured Soviet-made weapons home and, like Metcalf, were not punished. Only four Marines who ignored amnesty offers and tried to smuggle and sell their weapons were charged, Lehman said. Three have been court-martialed; the fourth has not yet been tried.

He did not defend the jailing of five Army soldiers who, unlike the Marines, do not come under his authority.

Army officials have said the five also ignored amnesty offers before being court-martialed, fined, jailed and discharged.

"An impression has been left that different cases within the Department of the Navy were handled differently," Lehman said in his letter to Rep. Les Aspin (D-Wis.) and Sen. Barry Goldwater (R-Ariz.), chairmen of the House and Senate Armed Services committees. "That is not the case. Each individual case was handled on its own merits, and all were handled consistently and appropriately."

The letter, sent yesterday, was released by the Navy.

Metcalf, now deputy chief of naval operations for surface warfare, has not commented since it was disclosed last week that he and his staff brought 24 AK47 automatic rifles home from Grenada on Nov. 3, 1983.

The vice admiral, then commander of the 2nd Fleet, had led the Oct. 23 invasion of that Caribbean island.

When Metcalf's Navy plane landed in Norfolk, customs officials seized the rifles because their importation violated federal law and military regulations.

Metcalf said he was unaware of the law and had brought the automatic weapons back as souvenirs. He received a "nonpunitive letter of caution."

In his letter yesterday, Lehman said Metcalf's "unfamiliarity" with the law "was deficient for an officer of his grade and responsibility." But the secretary also said Metcalf "is a dedicated and effective military officer and has my complete confidence."

Capt. Brent Baker, a Navy spokesman, said Marines who participated in the Grenada operation were given at least two opportunities to turn in captured weapons, once as they sailed from Grenada to Beirut and again on the return trip. Scores of Marines threw their weapons overboard, he said.

In addition, Lehman said that 60 pistols and 270 rifles turned in by Marines were rendered inoperable and returned to them as "war trophies." No AK47s were included, however, since captured machine guns may not be brought into the United States under any condition.

"The Marines who were court-martialed were found guilty of far more serious charges," Lehman said, including attempted sale and theft of U.S.-made weapons. "They ignored repeated orders to turn in war trophies for registration and compliance which were accompanied by offers of amnesty."

Navy officials also said the Marines and soldiers "stole" their captured guns from arsenals on the island, while Metcalf "requisitioned" his.

Army Capt. John Dorsz was jailed for taking five AK47s home. He said he planned to keep one; give two to his alma mater, the Valley Forge Military Academy, and give the other two to lower-ranking soldiers.

Dorsz did turn his guns in under an amnesty program managed by the federal Bureau of Alcohol, Tobacco and Firearms, according to testimony at his trial.

But Army investigators said they were not bound by that amnesty offer because they would have caught Dorsz anyway in the course of an independent investigation.