By a dramatic tie vote of 6 to 6, the District of Columbia City Council killed legislation yesterday that would have permitted adult adoptees to learn the identities of their natural mothers and fathers.

The outcome remained in doubt until Council Chairman Arrington L. Dixon, the last to vote, intoned the word "no," reversing the position he took April 10 when the council gave preliminary approval to the bill.

Supporters of the measure in the small audience said they were stunned. Some were members of organizations that had lobbied vigorously for passage of the bill.

"Many people are going to suffer for this by being denied access to something everybody else has-a complete birth certificate, said Terence Elton, an adoptee and member of a group called Adoptees in Search.

Yesterday's vote was a virtual rerun of what happened last Nov. 28, when the council-which then had its full complement of 13 members-voted 6 to 6 kill a similar measure.Dixon, then regarded as a supporter of the bill, was out of town on government business, and his absence speeled doom for the bill.

Under council procedure, approval of a bill requires a majority of those present. The council has one vacancy, leaving a current membership of 12.

Dixon said after yesterday's vote that he agonized over his position, but was persuaded by three women members of the council "who represent the poorer areas of the city east of the Anacostia River."

Opposition to the bill was led by Willie J. Hardy (D-Ward 8), who represents the contended that opening adoption records would break faith with natural parents-and especially young unwed mothers-who gave up their children for adoption.

The other two council members who represent neighborhoods east of the Anacostia, and who never wavered in opposing the bill, were Nadine P. Winter (D-Ward 6) and Wilhelmina J. Rolark (D-Ward 8).

Also voting in opposition yesterday were William R. Spaulding (D-Ward 5) and Jerry A. Moore Jr. (R-At Large).

Except for Dixion, all who voted against the bill had consistently opposed it during earlier deliberations.

Unlike the three hours of emotional debate on the bill April 10, yesterday's discussion was brief. It dealt chiefly with an amendment proposed by John L. Ray (D-At Large) that would have let natural parents apply to the city to keep their identities secret permanently. It also failed on a tie vote.

"There was no need for long, long debate (yesterday)," Hardy said. "I counted my votes, and figured we should get on with the voting."

Hardy said she was unconvinced by arguments of adult adoptees seeking to learn their roots. Approval of the bill, she said, 'would encourage people not to give children up for adoption, and it would encourage a lot of abortions."

Winter said her opposition to the bill was reinforced by a recent visit from a college student who had learned the identity of her natural father.

"The father was angry with the girl's mother and told her a lot of things that created problems," Winter said. "The more she (the student) talked, the more she had second thoughts, too."

Moore a Baptist minister in private life, said his confidential counseling with young, unmarried parents convinced him that discosure of parental identities would rip the social fabric.

The measure would have permitted adoptees 21 years old and over to apply to the city for the right to see birth records. A city agency would have sought the natural parents and would not have disclosed their identities without their approval.

On another matter, Hilda Mason (Statehood-At Large) was foiled in an attempt to win emergency passage of a bill to create a 90-day moratorium on the conversion of rental apartments to condominiums.

After the vote on the adoption information bill, only six members remained on the council dais-one member short of a quorum needed to conduct business and two short of the votes needed to adopt an emergency measure. After a 20-minute recess, no quorum could be assembled, so the council adjourned. Mason, usually genteel in manner, stalked angrily out of the chamber swearing at the absentees.