The Panamanian government yesterday called the U.S. Senate's ratification of the Panama Canal neutrality treaty "a historic moment for the country," but warned that it would study carefully a reservation the senate approved in its action on the treaty.

The reservation authorizes the use of U.S. military force in Panama and the government here said it will determine if that alters the treaty objectives or violates Panamanian sovereignty or integrity.

In a radio address to the country minutes after the Senate vote, chief treaty negotiator Romulo Escobar Betancourt said that Panamanian head of state Gen. Omar Torrijos sent a letter to President Carter yesterday outlining possible problems with the reservation.

Panama the Torrijos letter said will find "unacceptable any reservation that dishonors the national dignity, that changes the objectives of the treaty, or is intended to impede the exercise of Panama's sovereignty over all of its territory or the U.S. military withdrawal on December 31, 1999."

Governments spokesman said the letter referred primarily to the reservation proposed by Sen. Dennis DeConcini (D-Ariz.) and approved in 75-23 vote preceding the ratification approval.

The reservation authorizes both Panama and the United States independently to use military force in Panamanian territory should the canal be closed or its operations interfered with, even after the 1999 withdrawal date.

Panama has long objected to any provision of the neutrality treaty that would authorize a U.S. military presence here without Panamanian permission.

Torrijos was believed to be greatly angered by the proposed reservation. It puts him in the difficult position of explaining to the Panamanian people a possible eventuality - U.S. invasion of Panama should canal operations be interfered with - that he had promised them would not occur.

Escobar said Torrijos had received a letter Wednesday and a telephone call yesterday afternoon from President Carter explaining the additional provision and its probability of passage.

A lengthy radio explanation of the reservation, including a full reading of the texts of the Carter-Torrijos letters, was apparently an attempt to head off anticipated criticism here of the DeConcini provision and circumvent the need for an additional Panamanian referendum to approve it.

While pledging that the issue would be carefully studied, Escobar said that, in principle, the government considered the reservation "allowable" since it did not affect the "essence or content" of the treaty itself.

Specifically, he said, the reservation did not affect the scheduled 1999 closing of U.S. bases and complete withdrawal of U.S. troops stationed here.

Torrijos spent the day closeted with his Cabinet in the downtown house of a friend. Reporters converging on the scene after the Senate vote were told that Torrijos had "nothing to say" in addition to the Escobar statement.

While anticipated large-scale anti-treaty demonstrations did not occur, a small group of University of Panama law students paraded on the campus with banners reading. "No to the Right of Yankee Intervention in Panama." Students said the turnout - no more than 30 - was low because the university is currently in spring recess.

A spokesman for a group of Panamanian attorneys who have been outspoken treaty opponents said they would meet to compose a protest statement.

"We thing [approval of the DeCorcini reservation] was an elegant way for the Senate to reject the treaty," he said. The attorneys maintain, and the spokesman said the senators are aware, that the additional provision will require another referendum on the treaties here.

A referendum, required by Panamanian law, was held here last October and showed that 66 percent of the population approved the treaties. The lawyers said that the "wording the referendum question did not say anything about changes or reservations," and thus new provisions require a new vote.

In the U.S.-controlled Canal Zone, most ignored the final Senate debate until the last moment, when they turned on their radios to hear the live Southern Command Network broadcast. Canal company spokesman Al Baldwin said he "never saw [the Canal Zone] so quiet in my life."

While the predominantly antitreaty Zonians took the news of passage of the treaty in relative silence, the radio perhaps expressed the sentiment of some.

A country music broadcast following the end of the debate and vote began with a mournful song entitled "You can take this job and shove it, I ain't working here no more."