Senate Democratic leader Robert C. Byrd said yesterday that he had detected some national "shifting of opinion" toward approval of the Panama Canal treaties.

"What is required," he said, "is a better education of the public and for all of us . . . This will take some time."

The West Virginian and six other Democratic senators leave this morning on an Air Force jet to visit Panama and the Canal Zone. Republicans were invited but found the timing inconvenient, said assistant Republican leader Ted Stevens of Alaska.

Byrd said he thought the Senate Foreign Relations Committee, which held three weeks of hearings on the treaties to transfer the canal to Panama by the year 2000, probably would send the pacts to the Senate for consideration in January.

Traveling with Byrd are Democrats James Sasser (Tenn.), Spark Matsunaga (Hawaii), Walter Huddleston (Ky.), Donald Riegle (Mich.), Paul Sarbanes (Md.) and Howard Metzenbaum (Ohio).

Meanwhile President Carter renewed his plea to the Senate for support of the canal treaties.

In handwritten letters he pledged "my full effort to convince the American people that the agreement serves the best interests of the United States."

A White House spokesman said Carter sent letters to all senators except those considered firmly opposed to the treaty.