Senate Majority Leader Robert C. Byrd (D-W. Va) has called a press conference for this morning, apparently to announce his support for the Panama Canal treaties, with reservations.

The Carter administration has been counting on Byrd to help win Senate approval for the controversial treaties. Until now Byrd has said he was undecided, but several remarks in public have suggested that he was leaning toward approval.

Wednesday Byrd saw President Carter and Ambassador-At-Large Ellsworth Bunker, one of the negotiators of the treaties. Yesterday, he announced this morning's press conference, and the NBC program "Meet the Press" said Byrd would be its guest Sunday.

Byrd's latest public comments on the treaties came in a speech here Tuesday. He said the country should resist being carried away by "emotional jingoism" on the canal issue, a hint that he would take on the emotional opponents of the treaties.

In early December Byrd predicted that the Senate would approve the treaties, though said he remained uncommitted personally.

Both Byrd and Senate Minority Leader Howard H. Baker Jr. (R-Tenn.) appear to be moving in the same general direction on the treaties. On a visit to Panama last week, Baker said he could support them provided certain understandings or amendments were aded to the text.

Baker was particularly insistent that there be incorporated a pledge made in October by Gen. Omar Torrijos, the Panamanian leader, that the United States will retain a permanent right to defend neutrality of the canal and use it for the speedy passage of American warships in an emergency.

Byrd, too, has expressed concern on this point.

Panamanian officials have said they could accept an amendment or reservation of this kind.

A statement from Byrd today in favor of the treaties would add support to the Carter administration's view that Senate opinion is now moving in favor of the treaties. As recently as November there seemed a good possibility that 34 senators might vote against them - enough to prevent U.S. approval. But in recent weeks there have been no new converts to the negative side, and several senators - including Baker and Byrd - have moved toward approval.