In a decision that further jeopardizes the Equal Rights Amendment, the Justice Department said yesterday it will oppose efforts to get a speedy ruling from the Supreme Court on the constitutionality of the ratification process.

The National Organization for Women is seeking such an expedited ruling on grounds there will otherwise not be time to save the amendment.

The ERA ratification deadline is June 30, but in fact the clock is running even faster because many state legislatures have sessions that will end sooner.

A federal district judge struck down the ratification process as unconstitutional last month.

The Justice Department announced Monday that it planned to appeal the decision, but in a written statement released without clarification yesterday, the department added an important qualification, saying "the case is not ripe for decision."

"Ratification of the proposed amendment has not as yet occurred and will never occur if three additional states do not ratify the amendment by the . . . deadline. The department will oppose NOW's effort to expedite the appeal, since the entire matter may be rendered moot in the months ahead," it said. The department's announcement Monday encouraged pro-ERA women's groups; yesterday's sorely disappointed them. The department did not explain how it came to spell out its position in two separate announcements a day apart. The administration has opposed the Equal Rights Amendment in the past.

The department said yesterday its appeal was "consistent with statements by Attorney General William French Smith calling on the courts to exercise judicial restraint. The department at this time is not taking a position on the merits" of the amendment itself, which would outlaw all discrimination based on sex. NOW plans to file its request next week, and the Supreme Court could grant an expedited review against the wishes of the Justice Department.

Ironically Sandra D. O'Connor, the first woman Supreme Court justice, may not be able to vote on the issue. She will be faced with a decision on whether she should disqualify herself because she was a member of the Arizona legislature and a sponsor of the ERA when it was introduced in 1973. Arizona is now a plaintiff in the case.

The Reagan administration has aligned itself with conservatives in its opposition to the ERA, and yesterday a letter signed by 22 leaders of major conservative groups was sent to the president asking him to "instruct the Justice Department to shelve" plans for the appeal.

"The Justice Department is under no obligation whatsoever to defend the unfair ERA time extension which was lobbied through Congress by the Carter administration. If the Reagan administration truly believes in state's rights, then states should be allowed to decide for themselves how they are to be counted on approval or disapproval of a constitutional amendment," the letter said.

Its signers included Phyllis Schlafly of the Eagle Forum, Terry Dolan of the National Conservative Political Action Committee, Jerry Falwell of the Moral Majority, Howard Phillips of the Conservative Caucus, and Rep. Mickey Edwards (R-Okla.), who heads the American Conservative Union.

Tom DeCair, a spokesman for the Justice Department, said the White House had discussed the issue with the department yesterday, but had not influenced the decision. Sources at Justice say that although the administration does oppose the ERA, the issues in this case deal more with the mechanics of amending the U.S. Constitution.

At the center of the controversy is a Dec. 23 ruling by U.S. District Court Judge Marion Callister in Boise, Idaho, that Congress exceeded its constitutional authority when it voted in 1978 to extend the deadline for ERA ratification and that states that have already ratified the ERA have the right to vote to rescind that ratification.

The suit was brought in 1979 by the states of Idaho and Arizona against the General Services Administration, which had failed to remove five rescinding states from the list of ratifiers. The Justice Department was brought into the case to defend GSA and NOW later entered as a defendant.

Even before the Callister ruling, women's rights advocates were not optimistic about the chances of the amendment passing. Thirty five of the required 38 states had ratified the amendment, but five states had taken actions they claimed rescinded the earlier ratification.

Callister is a member and former high-level official of the Mormon Church, which has taken an official position against the ERA. In 1979 the Justice Department filed a motion to disqualify Callister from the case because of the appearance that he might not be impartial in the case, but he refused to step down.

NOW has charged that Callister delayed his decision until just before the January openings of many state legislatures, which makes it difficult to get a Supreme Court ruling in time to affect those states because of their short sessions. For example, among the unratified states, the Utah legislature adjourns Jan. 31, Georgia on Feb. 20, Virginia on March 13 and Florida on March 18.

In his opinion, Callister found that states do have the right to change their minds about constitutional amendments, and that they may do so until the amendment is actually adopted.

However, he did not deal with the issue of what exactly constitutes a recision and whether the five states had rescinded their ratifications.

There are major questions on the recisions. In two states, the recision vote was vetoed by the governor's office. In another, the state legislature voted an "annulment" motion after legislators couldn't get the votes to rescind. In a fourth, the legislature rescinded by a simple majority, a single vote in the Senate, even though a two-thirds majority was required for ratification.

Laurence Tribe, a Harvard University law school professor who specializes in constitutional law and is the lead lawyer in the NOW appeal, says all five states "sought legal opinions over whether they had the power to rescind. In each case, they were told there was no such thing as recision" in the constitution.

Callister also complained that Congress changed the deadline by a simple majority vote. He said that even if Congress had been correct in extending the deadline, it would have required a two-thirds vote.