The Senate, pleased with its debut on national television, voted 78 to 21 last night to keep the cameras permanently.

Although it took the Senate 40 years to come to grips with the radio and television era, the debate over whether to continue gavel-to-gavel broadcasting of floor proceedings had the suspense of one of the chamber's fabled quorum calls.

With the vote a foregone conclusion, most of the day was preempted by speechmaking on other issues, ranging from South Africa to U.S. monetary policy -- and, to no one's surprise -- by countless quorum calls.

With cable television tracking every minute of what had been repeatedly heralded as a historic day for the Senate -- the building of "an electronic bridge to the American people," as Majority Leader Robert J. Dole (R-Kan.) put it -- the floor was nearly empty for hours at a time.

For senators who have grown accustomed to the bright lights and ever-present robot cameras swooping around from their perch on the edge of the gallery rails, the novelty of the whole thing had long since worn off. Even some of the telegenic blue suits, blue shirts and red ties have been retired in favor of seersucker and pastel stripes.

After 2 1/2 months of experimentation, including seven weeks of live broadcasting, there were a few new rules proposed to deal with proper senatorial conduct before the cameras. One, aimed at curbing what critics called "show-and-tell" performances with charts, graphs and once even a display of cheese, would precisely restrict the size, number and placement of visual props. Other problems, such as the yellowish-green back wall that made some senators look as though they were "standing in split pea soup," as Dole described it, are still to be resolved.

But televising the Senate was "very clearly . . . an idea whose time has come," as Sen. William L. Armstrong (R-Colo.) put it.

Armstrong and other proponents of televising the Senate contended that cable broadcasting of Senate sessions, coupled with network use of brief segments, has expanded public understanding of the institution without threatening hallowed if arcane traditions.

To buttress their case, they cited a recent study by the Library of Congress' Congressional Research Service (CRS), which said, "Television coverage has changed the patterns of the Senate floor activity very little."

Dealing gingerly with the Senate's oft-repeated claim to be the "world's greatest deliberative body," the CRS observed, "The results of this study show the Senate to be a selectively deliberative body rather than a generally deliberative one. Most of the Senate's floor time was and continues to be spent considering only a few measures at great length."

But foes such as Sens. Russell B. Long (D-La.) and William Proxmire (D-Wis.) warned again yesterday that television would almost certainly harm the Senate.

Citing the same CRS report that proponents used, Long noted that speeches on miscellaneous issues have increased 250 percent since the advent of television, inspired largely by desires for reelection or election to "higher office." His concern, Long said, was that television would lead to "an increase in political expedience at the expense of statesmanship."

Proxmire, describing television as the "Che Guevara of modern society," warned that it would "make it easier for demagogues in Senate elections." In an apparently contradictory vein, he also recalled a recent afternoon of back-to-back quorum calls when senators were off the floor negotiating on budget issues. Viewers looked for an exciting debate and "what they got was boring, boring, boring," Proxmire said.

Still to be resolved is a Rules Committee proposal to ban the use of videotapes for political or commercial purposes, which some senators fear would apply to them but not to potential challengers.