It was 7:30 p.m., lights were ablaze inside the U.S. Capitol, and it appeared to be just another night for the overworked Congress toiling away on public business.

The Senate was in session, its armada of attendants standing by.

Capitol police and doorkeepers lounged about. Subway and elevator operators were at their posts. Support staffers stayed at their desks, switch panels and kitchen grills.

In the Senate chamber, the galleries were barren, but two members were on the floor, working doggedly into the night last Monday.

Sen. J. James Exon Jr. (D-Neb.) had to be there. He was the presiding officer. Majority Leader Robert C. Byrd (D-W.Va.), who runs the place, was there because he wanted to be.

Rather than turning off the lights and sending the hired help home, Byrd was reading to Exon, etching another of his unusual little Senate history lecturers into the official Congressional Record.

Since he sort of stumbled onto the idea last March, trying to entertain a visiting granddaughter and her classmates in the gallery, Byrd has delivered 28 of these anecdotal excursions through history.

A week after Byrd gave his first lecture on how the Senate operates, another granddaughter showed up. There was another legislative lull on the floor, so the senator gave another little extemporaneous talk.

It was clear by then that he was onto something. Other senators encouraged him to go on with more, and he did.

Byrd, explaining how it all began, said he thought his lectures "might be useful to senators in the future, and to historians, and to students in the universities, colleges and high schools around the country."

And with the Senate's 200th anniversary coming in 1989, he said, he explications of institutional procedure, protocal and personality might be of interest.

Byrd's "civic classes," as some Senate staffers facetiously call them, have provoked as much derision as praise around Capitol Hill, for the senator's outlook is decidedly not critical.

But for the careful listener, the early Byrd lecturers contain fascinating tidbits about the art work, the Latin phrases on the walls, the parliamentary gambits and terms, the meaning of the quorum bells.

Byrd is a stickler on procedure, but his exuberance has gotten the best of him several times. Nobody called him on it, but by addressing the galleries in the first two lectures, he probably violated a Senate rule.

Another time, demonstrating how a quorum call is made, Byrd was gently reprimanded by the presiding officer, Sen. Paul Tsongas (D-Mass.). Byrd kept talking during the quorum call -- a no-no.

For genuine political groupies, the early Byrd lecturers have plenty of grist -- lots of names, personalities, quirks. In one, he noted modestly that both he and Shakespeare had been meatcutters, and that he and Thomas Jefferson shared commonality as fiddle players.

Byrd's later lecturers have been more formal, prepared with the help of the Senate offices that he chooses to talk about and eulogize. He has discussed the leadership structure, party hierarchies, the parliamentarian, the secretary, the sergeant at arms, the pages and the chaplain.

The lecture that kept the Senate support staff working overtime last Monday was a panoramic reprise of the Senate press gallery and the literary lights who have populated it over the years.

Byrd's office denies there is any such intention, but most people around the the Senate believe that the collected history lessons will eventually become a book.

At least two senators, Jesse Helms (R-N.C.) and David Pryor (D-Ark.), suggested publication of an anthology.

No one, not even Byrd, is certain how much longer the lecture series will go on. What is certain, however, is that history has a price. The 127 pages Byrd's talks have filled in the Congressional Record, at $413.19 per page, so far have cost taxpayers about $52,475.