The Panama Canal treaties received nearly unanimous support in the Senate Foreign Relations Committee yesterday.

It appeared likely that 14 of the committee's 15 members will vote to recommend the treaties to the full Senate, providing they are modified in a way the Carter administration and the government of Panama have said is acceptable.

If this is the final committee vote, chances for a two-thirds majority of the Senate endorsing the treaties would be extremely good. It now seems possible that more than 70 of the 100 senators will vote to approve the treaties.

As recently as early December, the treaties still appeared to be in grave jeopardy in the Senate. Several senators on the Foreign Relations Committee said yesterday they perceived a change in the political atmosphere recently.

"In recent weeks . . . people are really beginning to think," said Sen. Charles H. Percy (R-Ill.), who announced his support for the treaties Wednesday.

But senators remain nervous about their constituents' reaction. Apparently, every senator's mail has run heavily against the agreements. Majority Leader Robert C. Byrd (D-W.Va.) indicated yesterday he would do all he could to deal with this problem.

In testimony to the Foreign Relations Committee, Byrd revealed that he has persuaded President Carter to make two televised addresses on the treaties, the first a fireside chat next week. Anxious senators hope Carter will make it easier to support the treaties by persuading more Americans of the merits.

Moreover, Byrd has worked out a special parliamentary procedure that will allow every senator to share in credit for amending the treaties.

The procedure will be to forward the pacts from the Foreign Relations Committee to the floor with the recommendations for amendments from the committee, but without formal action to amend them.

The full Senate will then be able to decide which amendments, reservations or understandings it wants to add to the treaties.

Byrd and Minority Leader Howard H. Baker Jr. (R-Tenn.) plan to cooperate in efforts to limite these modifications to the minimum necessary to win two-thirds approval.

It may be sufficient to add two amendments incorportating the language of an Oct. 18 communique issued by Carter and Gen. Omar Torrijos, the Panamanian leader. That communique spelled out America's perpetual right to defend the neutrality of the canal with military force, and to move U.S. warships to the head of the line to pass quickly through the canal in an emergency.

Torrijos has said he would accept these amendments.

Baker has also indicated that he might favor eliminating an article of one treaty which would commit Panama to permitting the United States to build a new, sea-level canal in that country, in return for an American pledge not to build one in any other country. Sources close to Baker said that if enough other senators insist on dropping that provision as a price for their support, he will back such a change.

Baker yesterday made his strongest personal statement in favor of Senate approval. "I have no reservation about the treaties," he said. "I think that ratification of the amended treaties is in the best interest of the United States."

Sen. Joseph R. Biden Jr. (D-Del.) praised Baker yesterday for contributing to the emerging Senate consensus behind the treaties."It took a great deal of courage to do what he did," Biden said of Baker, "frankly more than any of us."

Baker is presumed to be a possible Republican candidate for President in 1980 or 1984, and his support for the canal treaties invites opposition from the right wing of his party.

Sen. Robert P. Griffin (R Mich.) was the only member of the Foreign Relations Committee to announce his opposition to the treaties. Griffin called the pacts "fatally flawed," and said the Senate should give President Carter just "advice" - not advice and consent - on the treaties by advising him to renegotiate them entirely.

Every other member of the committee indicate support except Dick Stone (D-Fla.), who has remained neutral and avoided an opportunity to make a statement yesterday.After the hearing, Stone went to the White House for a meeting with Carter, and there were strong indications that he will announce his support for the treaties today.

Stone will also propose reservations to the treaties regarding the Panamanian government's policies on human rights, according to a reliable source.

Yesterday's hearing began with testimony from Byrd urging the committee to act favorably on the treaties. He promised to work actively for them, and spoke candidly about the political problems.

"Any senator who votes for these treaties will have some of the skin taken off his political nose," Byrd said. But he added the more optimistic thought that the public will eventually see the merits of the treaties "as people become better informed."

Today the committee is scheduled to "Mark up" the treaties by acting on all the proposed amendments it has received. Committee employees said this could be completed in one all-day session.