The Senate Foreign Relations Committee yesterday on a new article for one of the Panama Canal treaties. Supporters hope it will convince two-thirds of the Senate to approve them.

The new article incorporates a communique issued last Oct. 14 by President Carter and Gen. Omar Torrijos, the Panamanian leader, into the previously negotiated "neutrality treaty."

In the communique the two leaders stated that the United States retains a permanent right to defent the canal's neutrality and to send the U. S. Navy through in an emergency without waiting in line.

Adoption of this new article was the Foreign Relations Committee's major accomplishment in a desultory day of "marking up" the Panama treaties. Despite the supposed drama and importance of the treaty debate, rarely was a majority on hand. The committee will resume work Monday morning.

In another development, President Carter sent and released a letter to Sen. Dick Stone (D-Fla.) restating traditional American policy in Latin America, and informing Stone that Panama plans to hold elections for its national assembly next August.

Carter wrote Stone that the United States "will continue to play a visible and dynamic role" in Latin America, and will continue to oppose any Soviet effort to establish military bases in the area.

Stone hailed the letter as an important breakthrought, and said," I have been negotiating for this for three months."

The fact that Carter sent the letter and released it as "official policy," Stone said, would "probably" enable him to vote for the treaties in the Senate.

Stone had been officially undecided on the treaties, though administration lobbyists have long been counting on his support. Officials in the State Department and White House went out of their way to satisfy Stone's demand for the letter and public statement. Thursday they arranged a 30-minute meeting between Carter and Stone at the White House.

Stone said Carter had revealed an important now fact in writing him that Panama had announced that elections for the national assembly would be held on Aug. 9 of this year. In fact, these elections have been expected for months, and were formally announced early this month, according to the Panamanian embassy here.

The amendment approved by the Foreign Relations Committee yesterday will be forwarded to the full Senate as a recommendation, not part of the treaties as might ordinarily be expected. For handling these treaties, Sen. Robert C. Byrd (D-W. Va.), the Majority Leader, has decided on a new procedure that will enable all senators on the floor to share credit for amendments.

The administration acquiesced in the amendment the committee approved yesterday. Torrijos, the Panamanian leader, told committee Chairman John J. Sparkman (D-Ala.) in Panama that he too could accept an amendment based on his communique with Carter.

The treaties need two-thirds Senate approval, which means 67 votes. Byrd is obviously hoping to get more than 70, so that no individual senator can be held responsible by his constituents.

An administration lobbyist predicted privately yesterday that the final vote would be 69 to 31.

This official, afraid of undue optimism as a result of the expected 14-1 approval from the Foreign Relations Committee, predicted a very close fight when the treaties reach the floor.

The administration is especially worried that the Senate will add so much in the way of amendments, understandings and reservations that the treaties will be unacceptable to the Panamanians, or that in new plebiscite in Panama will be required.

The Foreign Relations Committee appeared sympathetic to the administration on this point yesterday. It voted down a series of amendments to the treaties proposed by Sens. Bob Dole (R-Ken) and Barry Goldwater (R-Ariz).

These amendments would have permitted the United States to station troops in Panama after the year 2000 (when the canal will revert entirely to Panama under the treaties); allowed U.S. negotiations with other Central American countries about building a new, sea-level canal; reduced American payments to Panama under the treaties by half or more, and forbidden the staioning of any foreign troops in Panama between now and 2000 (the treaties forbid them after that).

All were overwhelmingly rejected by voice votes.

The only opponent of the treaties in the committee is Sen. Robert P. Griffin (R-Mich). When yesterday's meeting was slow in starting for want of sufficient members, he complained that the apparent lack of interest "reflects on the committee and on the Senate." CAPTION: Picture, [WORD ILLEGIBLE] Sens. Howard Baker, Charles Percy and Frank Church, By James K. W. Atherton - The Washington Post