The Senate yesterday ended its days as the "invisible half of Congress," making its live, nationwide television debut in a six-week experiment that leaders agreed would almost certainly lead to permanent broadcasting of proceedings.

Senators preened, postured and partied to mark what was widely described as a "historic" milestone in chamber history. The event prompted a few veiled warnings against excesses and a parody from Sen. John Glenn (D-Ohio), who invited cameras to zero in on his bald head as he gave colleagues a demonstration in the art of applying pancake makeup.

Both Senate Majority Leader Robert J. Dole (R-Kan.) and Minority Leader Robert C. Byrd (D-W.Va.) said they had little doubt that the Senate would make television a permanent part of its proceedings when it votes on the issue late next month.

But Dole also warned colleagues to "resist the temptation to exploit technology" and, in comments to reporters before the session, acknowledged that the Senate has a few problems in coping with the challenge of television, such as "explaining why we have 30-minute quorum calls."

Glenn, normally one of the Senate's more serious members, had apparently had his fill of media consultants' advice on how to perform on the tube. So he took the floor with pancake makeup, a mirror and TV-style red tie (carrying it, not wearing it), even pointing his balding head at the cameras at one point to illustrate what senators had been told not to do. Other senators, especially those with thinning hair, had been assiduously holding heads high to get the cameras to focus on something other than their shiny scalps.

Glenn seemed to be having such a good time that he was jerked back to his desk, yo-yo fashion, when he walked away from it with his microphone still attached to his suit jacket.

There was even a poem for the occasion from Sen. Howell Heflin (D-Ala.), who appeared to share Glenn's amusement at the event. "Turn the spotlight over here; focus the camera at my place; pages, please don't come too near; otherwise, you just might block my face," the ode began.

In all, the Senate's debut on television was low-key, uncontentious, even a bit ponderous as the gavel fell at 2 p.m. and the Senate burst onto screens across the country, by way of a special new channel on C-Span, the cable network that also televises House proceedings.

No more than 10 of the 100 members were on hand for the march into the television era, most -- including Dole -- appearing in the regulation dark suit and red tie. Even the lure of television, it appeared, was not great enough to get a full complement of senators to hustle back from the 12-day Memorial Day recess for the start of business.

Some senators used the spotlight to argue for favored causes, from continued compliance with the SALT II treaty, which the Reagan administration has announced it may discontinue observing, to Individual Retirement Accounts (IRAs), which would be curtailed by the tax overhaul bill that the Senate will consider later in the week.

After an uncharacteristically brief (about two-minute) quorum call, the Senate got down to routine business: consideration of a relatively noncontroversial bill to continue programs affecting higher education.

But, mainly the day was devoted, in comments both on and off the floor, to extolling the virtues of television and expressing hope it will force the Senate to "shape up its act," as many senators have expressed it.

On the floor, the tone was set by Dole, who called it the "day when the United States Senate catches up with the 20th century," as it joins the House in the television era and ends its obscurity as Congress' "invisible half." One element that may make the Senate even more visible will be the availability to network news shows of the C-Span film of the proceedings.

Off the floor, the center of attention was former majority leader Howard H. Baker Jr. (R-Tenn.), whose often lonely fight for television in the Senate did not achieve results until after he retired in 1984.

Baker acknowledged that the Senate may never "replace 'Dallas' " as a viewer favorite but said he had no doubt that the country will "love the Senate," as he put it. "It the Senate is very special . . . . It's populated by the choicest characters in the whole political spectrum," he said.

Dismissing suggestions that television may adversely affect the Senate, he said, "It won't affect the Senate, but it will affect the country's perception of the Senate." As for himself, he said he had "the best of all worlds -- I can sit there and watch; I don't have to do it."