Invoking its legally challenged emergency powers for the 89th time this year, the D.C. City Council voted yesterday to extend the six-month-old moratiorium on condominium conversions for another 90 days.

The council took a related action that could result in keeping the near-total moratorium in effect until late next summer, giving the council time to act on a proposed permanent law regulating the future conversion of rental apartments into condominiums.

Conversions have become a volatile political issue in the city, with a recent study estimating that nearly 25,000 apartments -- about 12 percent of the rental housing stock -- have been converted or are in the process.

Yesterday's passage of a third emergency bill temporarily blocking conversions comes at a time when the council's use of its emergency lawmaking powers in under judicial and congressional attack.

The D.C. Court of Appeals will hear arguments Monday on a Superior Court judge's ruling that the council misused its emergency power in July when it passed the existing moratorium bill for the second time. Superior Court Judge George H. Revercomb, who issued the ruling, permitted the moratorium to stay in effect until the appeals court could rule.

The moratorium that was voted in July will expire Sunday. The new emergency bill will take effect Monday, the day of the appeals court hearing, if it is signed into law by Major Marion Barry. There was no word last night on his plans.

Since the city's 15 percent interest ceiling was set by a procedurally similar second enactment of emergency legislation, Revercomb's ruling caused major mortgage lenders recently to cut off home loans in the city for two weeks.

Congress quickly passed a bill validating the 15 percent ceiling. President Carter signed this legislation yesterday, and lending officials said all 66 mortgage banking firms operating in the city, as well as about 12 of the 16 savings and loan associations are expected to begin making loans again by this morning.

The city's Home Rule Charter, which took effect in 1975, requires that legislation passed by the council be sent to Congress for a review that takes at least six weeks and often much longer. To put bills into effect immediately for 90-day periods, the council almost routinely declares emergencies, as it did yesterday for the 89th time this year.

Before acting yesterday, the council was advised by its chief lawyer, James M. Christian, that its power to act was not blocked by Revercomb's ruling. Council Chairman Arrington Dixon observed that "we have been orchestrating this [moratorium extension] . . . We are on top of it."

Passage of the emergency extension was by voice vote, with only Betty Ann Kane (D-At-Large) opposed. She said later that continuing an indefinite-moratorium "is not in the best interest of . . . preserving rental housing."

After approving the emergency bill, which could be struck down by the appeals court, the council voted preliminary passage of another bill sponsored by David A. Clarke (D-Ward 1) that would create a further 180-day conversion moratiorium. It did so by the procedure that requires a congressional review.

If final passage is voted Dec. 4 and the bill is signed by the mayor and allowed by Congress to go into effect, it would extend the moratorium until next August or September.

In the meantime, the council will consider a strict bill to establish permanent controls over condominium conversions that was introduced last week by 9 of the 13 council members.

In other actions yesterday, the council:

Confirmed the mayor's nominations of Herbert Simmons Jr. as director of the Office of Consumer Protection after Wilhelmina J. Rolark (D-Ward 8), who had blocked action previously, said she was satisfied with Simmons' qualifications.

Approved the proposed $1.5 billion budget for the 1981 fiscal year with few changes from the version proposed by the major. The biggest change was adding $3.9 million for the public schools to the $237 million sought by Barry. Congressional action still is needed.