The Senate yesterday offered a sneak preview of what it might look like on television: the legislative equivalent of an encounter-group session, punctuated by long pauses for quorum calls.

Even if the Senate was not ready for prime time, its opening debate on a bill sponsored by Majority Leader Howard H. Baker Jr. (R-Tenn.) to permit televising of Senate sessions did produce a spate of senatorial-style soul-searchings for the few onlookers in the galleries.

"What is our justification for existence?" asked Sen. John C. Danforth (R-Mo.) in opposing the proposal. "Is it to debate great issues of public policy or to dream up 'one-liners' suitable for 60-second slots on the evening television news shows?"

"Whether we like it or not, we are what we are," responded Baker in kind, saying that the Senate is a "cross section of our constituents" and should not be hidden from them.

Finally, as evening approached, Sen. Russell B. Long (D-La.), rumored to be planning a filibuster against the proposal, took the floor to warn that televising the Senate would do little more than make its members more verbose.

Had the Senate been on television during its debate on repeal and then restoration of the minimum Social Security benefit, what senator could have resisted speaking when all those "dear old people" were watching and listening, Long asked.

None, he responded, including himself. "I'd have had to be in it," he said, even though his intercession might not have changed a vote.

Long was not the only senator to acknowledge a tendency to succumb to the temptations of television.

There was a time, Danforth said, when committees on which he served were considering, simultaneously, the financial problems of Bert Lance, former president Carter's budget director, and an important tax bill. The Government Affairs Committee session on Lance was televised, while the Finance Committee tax session attracted "The Wall Street Journal, The Washington Post and Petroleum World," he recalled.

"I should have spent all my time in the Finance Committee," Danforth said, "and I didn't." That, he said, "is what politicians do."

There was also talk of quaint Senate customs, widely observed but seldom discussed in polite company, such as speeches that are never given yet are entered in the Congressional Record. Every word uttered on the Senate floor winds up in the Record, along with "some words that are not uttered," Danforth noted.

Rules Committee Chairman Charles McC. Mathias Jr. (R-Md.) disputed what he called the notion that senators are just "a hundred moths attracted to this candle of televison," and suggested that the public would get more from seeing the Senate than just reading about it. "It's the exchange, the fire in your eyes, the lilt in your voice," he said.

Baker contended that television would sharpen debate rather than lengthen it, describing televised sessions as the "next and best step we can take to restore to the Senate the quality of a great forum of public debate."

By the end of the day, the Senate had agreed to nothing more than a vote Thursday on a motion to proceed with the bill, meaning that the issue may not be resolved soon, especially if Long and his allies keep talking. Other measures will be "double-tracked" with the television measure, so it will not bog down the Senate indefinitely.

The measure merely authorizes television and radio coverage of the Senate, probably not before next year, with detailed procedures for control and operation of cameras left up to the Rules Committee and another Senate vote. The committee estimated that the total cost could approach $3.5 million if the Senate runs its own system. House proceedings have been televised since 1979.

Aides to Baker say the majority leader has enough votes to break a filibuster, although probably not on the first try. However, Long was reported yesterday to be picking up Democratic support for his position.