''It is the end of the judicial line in the United States of America. Cases flow here from the federal courts, they flow here from the state courts. There isn't any other place to go once we make a decision here.''
The words are Harry Blackmun's. And he is talking about the United States Supreme Court, America's court of last resort, where he serves as an associate justice. Mr. Justice Blackmun, along with high tribunal colleague William H. Rehnquist, make rare television appearances on an ABC News ''Closeup'' documentary on the Supreme Court (Saturday, Dec. 29, 10 to 11 p.m. EST).
The chance to watch usually camera-shy high-court justices discuss their work on network television is probably reason enough to watch this program. But it has other things to recommend it, too, including frank discussions of highly volatile issues that the court faces today - ranging from school prayer to the rights of criminal defendants to relatively new ''ethical'' issues involving life-support systems and government intrusion into family and private matters.
Using legal experts, government spokesmen, and vivid graphics (chanting children, animated parents, policemen making arrests, and heart-wrenching hospital scenes), this documentary races through a spate of issues in half as much time as the court allows for oral arguments in a single case dealing with but a specific aspect of one of these subjects.
Senior producer Richard Richter confides that there had been serious consideration of narrowing the scope of the documentary and concentrating on only one ofthe so-called ''new'' issues facing the court - that dealing with so-called ''life and death'' questions, such as abortion and the use of mechanical means to prolong life. But important decisions by the court last spring regarding the separation of church and state, as well as those that tended to restrict the rights of individuals accused of crimes, gave ABC pause. And it was finally decided to take an overall look at the direction of the court.
The result: a production somewhat lacking in focus and clarity but one that ably captures the role of the Supreme Court. To some extent, the vagueness is excusable. ''Closeup'' examines a court whose judicial philosophy defies classification, in the view of many. And some critics would even go so far as to charge that there are decisions of the present Supreme Court that are unfocused and unclear.
Regardless, ABC plays it pretty straight - and deserves credit for a balanced production. The court is neither praised nor condemned. But if one is looking for a definitive critique, it won't get it here. Or if the expectation is a perceptible clash of judicial philosophies, there will be disappointment. Justices Blackmun and Rehnquist maintain their courtroom dignity - although gently goaded by the usually cantankerous Harvard law professor Arthur Miller (of ''Miller's Court'' fame).
What does come through is that the Supreme Court is faced with increasingly complex and delicate social and legal questions that force the justices to balance individual rights guaranteed by the Constitution with equally crucial responsibilities to a broader society.
Theirs is often a no-win situation with the media and the public. When the court has leaned toward protection of the individual, critics have charged that the public good, or collective safety, is put at risk. And when it has moved more broadly toward community protections - as the present court led by Chief Justice Warren E. Burger tends to do - civil libertarians have decried an abandonment of the Bill of Rights.
Over the years, the emphasis has gone back and forth. Professor Miller tries to prod a discussion about the swing of the pendulum today towards law and order. But Justice Rehnquist - acknowledged as the court's must conservative member - sidesteps an assessment of ''ideology.''
''There will continue to be thesis, antithesis, synthesis,'' he explains. ''That's the way any body like ours works. You push ahead some, you retrench some, you keep what seems sound. . . . And that's the way the court has worked for 200 years. It's very much a cyclical thing. . . .''
Perhaps the most vivid dramatization involves school prayer. The court is due to decide several cases in this highly controversial area early in 1985; the rulings could significantly alter long-established religion-in-the-classroom practices. Justice Blackmun cautiously avoids assessing whether long-held church-and-state precepts are being damaged. But he allows that the so-called wall of separation ''is certainly not a wall that is without scars.''
ABC originally invited all nine Supreme Court justices to take part in this presentation. Only two accepted. Justice Rehnquist requested a review of his part of the script. The network agreed but said that changes could result in deletion of all footage involving Mr. Rehnquist.