The Pentagon said yesterday it plans to examine whether it was fair to court-martial and order to jail seven lower-ranking soldiers and Marines for bringing back captured automatic rifles from Grenada when their commanding officer was not punished for trying to bring home 16 of the Soviet-made weapons for himself and his staff.

The investigation follows reports that Vice Adm. Joseph Metcalf III, who commanded the U.S. invasion of Grenada in October 1983, was only "cautioned" by the Navy after returning with the AK47 rifles despite federal and military prohibitions.

Deputy Defense Secretary William Howard Taft IV ordered the department's general counsel to make sure the cases were handled equitably. In a separate action, he asked for a report from Navy Secretary John F. Lehman Jr. on gun-smuggling allegations against Metcalf and two Marines, who fall under the Navy's jurisdiction.

Meanwhile, Common Cause, the self-styled citizens lobby, released a Navy document showing that Metcalf's superiors at Atlantic Fleet headquarters killed an investigation of the incident after Metcalf "requested that he be allowed to handle the problem himself," according to the document, whose authenticity was confirmed by Navy officials. Metcalf told investigators that he acquired the captured weapons as souvenirs and was not aware of the prohibitions against bringing back automatic weapons from combat areas, it said.

Then, according to the document, he asked investigators: "What is there to investigate?"

Capt. Brent Baker, a Navy spokesman, said that, despite charges by Common Cause, Metcalf was not allowed to investigate himself or quash the investigation. Baker said investigators merely sought his "side of the story" and reported it to his superiors, who "cautioned" Metcalf against bringing back automatic weapons but did not punish him.

Baker said it is unfair to compare Metcalf's treatment with the punishment meted out to the soldiers and Marines, who received jail terms as long as three years, because they smuggled the captured weapons into the United States, and in some cases sold them on the black market.

The Army also defended its strict punishment of five soldiers, including a captain, who returned from Grenada with AK47s and were court-martialed, fined, ordered jailed and dismissed from service.

"We have perfectly good rules, which the Army people broke and were punished for," Lt. Col. Craig MacNab, an Army spokesman, said. "If we condoned the introduction of automatic weapons into American society, you'd have our scalp."

MacNab said the five convicted soldiers received far less than the maximum penalty of 10 years in prison. Their cases automatically will be reviewed by higher military courts, even though four of the five men have completed or are serving their prison terms.

The Pentagon investigation, being conducted by General Counsel Chapman Cox, is aimed at determining whether the sentences given the lower-ranking servicemen were fair and whether Metcalf received preferential treatment because of his rank, according to Pentagon officials.

"It is important that the Uniform Code of Military Justice be applied equally," one official said. "It should not be bastardized because of rank."

Meanwhile, Taft, who is in charge of the Defense Department because Secretary Caspar W. Weinberger is traveling overseas, in his memo to Lehman asked for a "complete report" on the gun-smuggling allegations.

Taft said the report should discuss how each allegation was handled and what the ground rules were for bringing home enemy weapons from Grenada.

Earlier yesterday, Lehman issued a separate statement that he has reviewed the Navy's handling of Metcalf's case and those of the two Marines, has decided that they were "appropriate and considers the matter closed."

According to military regulations drafted at the peak of U.S. involvement in Vietnam in 1969, servicemen returning from combat duty may bring back certain "war trophies" and captured firearms. But the code rules out automatic weapons such as AK47s, which the Soviet Union supplied to Grenada's leftist government and to Cuban troops on the island.

The National Firearms Act prohibits importing automatic weapons, including AK47s, without proper authorization or license.

Metcalf, 56, a flamboyant and pugnacious military commander in Grenada, returned to his Norfolk base on Nov. 3, 1983, aboard a plane carrying 24 AK47s and 24 empty ammunition magazines, according to customs officials who boarded the aircraft after receiving what Pentagon sources said was an anonymous tip.

Sixteen of the weapons were tagged with Metcalf's name or those of staff members who accompanied him, sources said.

According to the Navy document obtained by Common Cause, customs officials seized the weapons and turned them, and the case, over to the Naval Investigative Service (NIS).

Naval investigators contacted Capt. James Brunner, staff legal officer of the Atlantic Fleet command, to which Metcalf reported. Asked if Metcalf's superiors wanted the case investigated, Brunner said Metcalf wanted to handle it himself, according to the document.

It also said that Brunner told investigators that Metcalf's superiors "suggested" that Metcalf "be contacted to determine if he desired further NIS assistance."

Metcalf told investigators he was "solely responsible" for the captured weapons aboard the plane and that he thought they could be legally brought into the United States as souvenirs as long as they were "inoperable," the document said.

A day later, it said, Brunner said that Atlantic Fleet officials "advised that no further NIS investigation was desired." The NIS probe was ended, and Metcalf later was given a nonpunitive "caution" regarding his actions.