A group of Senate Democrats, whose votes could be crucial to the fate of the Panama Canal treaties, are to hold face-to-face meetings this week with Panamanian leader Gen. Omar Torrijos and U.S. citizens in the Canal Zone.

Senate Majority leader Robert C. Byrd, (D-W.Va.), who will lead the group, said yesterday that the senators, mostly junior members of the body, will spend three days in the Central American country, meeting with a cross-section of those who support and oppose the treaties.

All but one of the eight or nine senators on the trip are undecided on how to vote on the treaties, Byrd said.

The votes of two-thirds of the Senate, or 67 members, are needed to approve the controversial treaties, already signed by Torrijos and President Carter. Byrd has repeatedly said the treaties, which would turn over control of the Panama Canal to Panama by the end of the century, would be rejected if they were voted on this year.

"This is going to be one of the most fundamental international relations issues of our times" and senators have a responsibility to make an on-site visit "so that we can base our decision on facts and not emotions," Byrd said.

A tentative list of those making the government-paid trip includes: Paul Sarbanes (D-Md.), Wendell Ford (D-Ky.), Walter Huddleston (D-Ky.). Spark Matsunaga (D-Hawaii), Daniel Patrick Moynihan (D-N.Y.), Donald Riegle (D-Mich.), James Sasser (D-Tenn.), and Howard Metzenbaum (D-Ohio.).

Byrd has yet to take a position on the treaties. He said yesterday that if he decides to back them he will become an aggressive advocate, but if he decides to oppose them he will do so quietly and simply "cast my vote as a senator from West Virginia."

Byrd also announced that the White House had asked him to select five senators for a two-week trip to China in January. Those invited to date are Sens. Alan Cranston (D-Calif.), Charles McC. Mathias (R-Md.), James Abourezk (D-S.D.) and Daniel K. Inouye (D-Hawaii).