Justice Harry A. Blackmun has indicated that the Supreme Court is not likely to overhaul its 1973 decision legalizing abortion.

The court surprised both sides in the controversy last spring when it agreed to consider two cases that were similar to cases it decided just two years ago. The action fueled speculation that the court might substantially alter, if not overturn, the 1973 decision.

But Blackmun, in a speech last month to federal judges in Little Rock, viewed the action differently.

"There are always four votes" to hear an abortion case, Blackmun said. "And the other five of us heave a deep sigh and wish we didn't have to go through this traumatic experience again."

Under court rules, a case is granted full review if four of the nine justices vote to do so. The two cases, which involve efforts by Pennsylvania and Illinois to regulate abortion, will be argued Nov. 5.

But it takes a majority to change or overturn a prior ruling, and Blackmun, who wrote the 1973 decision, apparently counts at least five votes on his side, despite the Reagan administration's urging that the 1973 decision be overturned. "A very amazing brief," Blackmun said of acting Solicitor General Charles Fried's arguments.

"The state legislatures," he added, "are constantly trying to push back the effect of Roe v. Wade and make it more difficult" to obtain an abortion.

The most recent abortion appeals -- in 1983 -- have been decided on a 6-to-3 vote; Blackmun did not say who provided the fourth vote to hear the latest cases.

Chief Justice Warren E. Burger, though a member of the original majority, is deemed the most likely fourth vote to hear the cases. That does not mean, however, that he will vote with the dissenters.

Blackmun said, "This court is not a great court, but I think it is not the worst court that we have had in history."

"It's a battle, it's not a picnic and it's plain hard work," Blackmun said. "If I had any sense, I think I'd step down."

Blackmun is not about to do so. He said he had received the following letter recently from a Phoenix lawyer: "Don't you think it is about time you retired to answer the call of the fishing and the hiking of the Northwest and permit the president to appoint somebody who is attuned to and will respond to his particular philosophical bent?"

Blackmun said he wrote back: "Dear Mr. So-and-So. No. Sincerely, Harry A. Blackmun." FRIEND OF THE MEDIA?

Burger has never been known as particularly fond of the broadcast media. He objected to television coverage of his annual speech to the American Bar Association and has staunchly opposed cameras in the courtroom.

But it seems the chief may have a soft spot for the print media -- or at least a small part of it.

Burger is setting up a $5,000 college scholarship trust fund at Johnson Senior High School in St. Paul, Minn., in the name of his former English teacher, Edna Moore. Burger, class of 1925, says Moore was adviser to the school paper when Burger was its editor and sports editor. FILLING COURT VACANCIES

The White House has announced that it plans to nominate Laurence H. Silberman, a former deputy attorney general and one-time ambassador to Yugoslavia, to the U.S. appeals court here.

Silberman, a Washington attorney who is a member of the General Advisory Committee on Arms Control and Disarmament, would fill a position created by Congress last year.

One other spot on the 12-member court has been vacant for nearly a year -- the opening created when Judge Malcolm R. Wilkey assumed senior status last December.

Attorney General Edwin Meese III this week told a conference of judges that the Reagan administration, which has been slow to fill federal court vacancies, will move quickly to try to fill 86 vacancies by the end of this year.

Sources said Washington attorney Marion Edwin Harrison, a leading candidate since January for Wilkey's seat, has not yet won the approval of the American Bar Association, which screens candidates for judgeships. Other candidates are being considered.