Jill Sinclair knows her Senate.

"I have a seating chart with the all names on it," said the eighth grader from Pittsburgh. "I studied so I would be able to tell who was talking. I wasn't ready for this, though."

Miss Sinclair was not prepared for the civics lesson she received this week. She and thousands of other luckless citizens who happened by the Senate visitors gallery watched Paul S. Sarbanes (D-Md.) put the right of free speech to the test with a four-day filibuster.

"I didn't know a filibuster could be so boring," said Leonard M. Paulson, who with his wife traveled to Washington this week from their home in Milaca, Minn. "If they made other senators sit there this would never happen."

But they don't. So Sarbanes spoke to an empty Senate chamber for most of the past week while unsuspecting visitors from all over the world -- many of them students dressed in their best clothes -- watched him try to block the passage of a bill that would transfer control over National and Dulles airports from the federal government to a regional authority.

To many Americans the mention of a filibuster brings to mind an impassioned image: a valiant Jimmy Stewart in "Mr. Smith Goes to Washington," using time and moral suasion to wear the opposition down.

But life is rarely so noble, and these days many filibusters -- designed as a tool for the minority to block action on a bill that seems destined to pass -- consist of senators reading from arcane legislation or rambling freely in deadening monotones, designed not to persuade, only to delay.

Here, for example, is Sen. Sarbanes holding forth on noise provisions in the law he opposes:

"All I can say is that this legislation allows it to happen, whereas current legislation precludes it from happening. It allows it to happen . . . . The Senator Paul S. Trible Jr. (R-Va.) says it will not happen . . . . If you really wanted to be sure that it would not happen, you in effect would not permit it to happen . . . . The fact that it is possible means that it may happen."

The only way to limit debate in such a case is to get 60 senators to agree to vote to cut it off. But the Senate is a body bound by tradition, and many senators are unwilling to cut short a filibuster on the first try. There have been attempts over the years to curtail -- or eliminate -- the right to filibuster, but the Senate has rebuffed them all.

Sarbanes survived his first cloture vote last Friday easily, 50 to 39. Only yesterday did his colleagues pull the plug by a vote of 66 to 32.

Of course, Sarbanes' dilatory tactic was nothing big in the annals of the Senate; Strom Thurmond (R-S.C.) established a one-man endurance record of 24 hours and 18 minutes without rest when filibustering against the 1957 Civil Rights Act. In 1905, South Carolina senator Ben (Pitchfork Ben) Tillman read Byron's "Childe Harold" to obtain a change in the southern states' civil war claims.

In 1935, Louisiana senator Huey Long kept his colleagues entertained during his filibuster of a bill to extend the National Industrial Recovery Act by reading recipes for "pot likker." Less imaginative legislators have resorted to reading telephone books and baseball statistics.

But no matter how time-honored the tradition, most visitors seemed to walk away from the Sarbanes show a little less excited about what goes on in Congress than when they came.

"I can't believe that happens," said Bettina Squerteig, a German college student here for a firsthand test of her knowledge of American history. "I had hoped to see a debate on the war in Nicaragua. I also wanted to see Senator Kennedy."

Patricia Komosinski, a Cleveland native now living in Japan, put it another way: "You have to see these things. Otherwise, who would believe it? I was impressed with Senate chamber, though. Just not with what was happening in it.