Supreme Court Justices Harry A. Blackmun and Sandra Day O'Connor have been on opposite poles on most major issues since O'Connor arrived on the bench in 1981.

But Blackmun now says he may have written off President Reagan's only appointee too quickly as a rigid, hard-line conservative.

Blackmun, reviewing the court's term in an Arkansas speech to judges from the 8th U.S. Judicial Circuit last summer, said he thought "the right, represented by the Chief Justice Warren E. Burger and Justice William H. Rehnquist, is more firmly together than it has been.

"In the past, I have put Justice O'Connor over there," Blackmun said, "but there have been a few little intimations that in certain areas she is becoming somewhat independent and her own woman."

Blackmun didn't say what the "intimations" were, and overall voting statistics don't show major changes in her views.

O'Connor agreed with Burger 84 percent of the time last year and with Rehnquist 87 percent of the time. That is a drop from the year before, when she agreed with each of them 91.9 percent of the time, but the most recent percentages are generally in keeping with her voting patterns in prior terms.

Blackmun may have been thinking about her votes in a few major cases last year, such as the Alabama public schools "moment-of-silence" case, in which O'Connor sided with the moderate-liberal group in ruling that practice unconstitutional.

Blackmun, a Nixon appointee in 1970, is himself a good example of a justice whose voting patterns changed dramatically during his tenure on the court. Blackmun's first year saw him voting with Burger about 90 percent of the time. Last year, he agreed with liberal justices William J. Brennan Jr. and Thurgood Marshall more than he voted with Burger and Rehnquist.

Blackmun, speaking to the judges in Arkansas, noted that the court will hear a case this term from their circuit. The case, Nix v. Whiteside, involves a lawyer's sometimes conflicting obligations to his client and to the court. The question is whether a lawyer who refuses to allow his client to commit perjury is adequately representing the client.

"I think we'll have some head-scratching on that one," Blackmun predicted. The case is being argued Tuesday.

Blackmun also commented on last term's decision involving RICO, the Racketeer Influenced and Corrupt Organizations Act. Lower courts had divided over whether the law allows private civil suits for treble damages against corporations that have not been convicted of racketeering.

Blackmun was on the losing side as the court ruled 5 to 4 to allow such suits. But he told the judges he felt Congress did not intend such a broad application of the law and that the issue "is a matter that the Congress must pay attention to to resolve."

END IN SIGHT . . .CIA general counsel Stanley Sporkin, whose quest for a federal judgeship resembles the travails of Sisyphus and the rock, is getting closer to his goal, sources said last week.

Sporkin's nomination to the U.S. District Court here has been held up for 16 months because of opposition from conservative senators including Jeremiah Denton (R-Ala.).

The Senate Judiciary Committee held an unusual closed-door session last week to hear allegations against Sporkin, including one that Sporkin improperly helped a Central Intelligence Agency official under investigation by the Justice Department for leaking classified information.

Sources said most of the 11 scheduled witnesses testified and cleared up many of the questions in Sporkin's favor.

The committee had scheduled Sporkin and the remaining witnesses to testify last Friday, but there was yet another delay, and Sporkin's testimony is now likely to be heard next week.

Sources said that barring new questions, Sporkin appears headed for confirmation.

In contrast, Jane Richards Roth, wife of Sen. William V. Roth Jr. (R-Del.), nominated last summer, breezed through the committee confirmation process despite some concern about her husband's direct conversation with President Reagan to support the nomination.

Roth, confirmed by the full Senate on Friday, is a Harvard Law School graduate and was a civil litigation partner in a firm founded by her grandfather