There were strong new indications yesterday that the Senate will approve slightly modified versions of the Panama Canal treaties by a two-thirds vote.

Sen. Howard H. Baker Jr. (R-Tenn.), the Senate minority leader, said he thought he could assemble a "package" of minor modifications to the treaties that would enable a majority of Senate Republicans to vote for them. If true, this would virtually insure two-thirds approval.

Baker said he had taken a headcount of GOP colleagues, but said he had a "good hunch" about how such count would turn out.

Senior administration officials spent much of Wednesday and yesterday in White House meetings to plan strategy on the canal treaties. According to one participant, the meetings ended on an optimistic note.

Sen. Lloyd M. Bentsen Jr., (D-Tex:), the Senate minority leader, said he thought he could assemble a "package" of minor modifications to the treaties that would enable a majority of Senate Republicans to vote for them. If true, this would virtually insure two-thirds approval.

Baker said he had not taken a headcount of GOP colleagues, but said he had a "good hunch" about how such count would turn out.

Senior administration officials spent much of Wednesday and yesterday in White House meetings to plan strategy on the canal treaties. According to one participant, the meetings ended on an optimistic note.

Sen. Lloyd M. Bentsen Jr., (D-Tex.) announced yesterday that he would support the treaties with minor changes. Bentsen had been undecided, and aides said his mail on the treaties was 26,000 against approval, 350 letters in favor.

An administration official said "four or five other undecided senators will soon announce support for the treaties.

No undecided senator has come out against the pacts in several months.

"It's really a question of timing now," a senior lobbyist for the Carter administration said last night, indicating the President would accept limited amendments to the treaties, but that if Senate consideration is put off too long, pressure may build to add an unacceptable number of changes or understandings.

Officially Carter will continue to oppose any amendments, sources said. But, they added, he is willing to see an amendment incorporating an agreement between himself and Panamanian strongman Gen. Omar Torrijos guaranteeing U.S. rights to defend the canal after the year 2000 and assuring priority passage to U.S. naval vessels in an emergency.