One of the first pieces of legislation to face the new session of the City Council this month will be a controversial measure that would open adoption records to adult adoptees seeking the identity of their birth parents and other information contained in court and adoption agency files.

The bill was defeated in a surprise 6-to-6 vote on its second reading in late November, after passing its first council test by a 7-to-2 vote two weeks earlier. A public hearing last April and the two council meetings have been marked by emotional and sometimes tearful arguments from witnesses and council members on both sides of the issue.

Council member Hilda Mason (Statehood-At Large), who introduced the bill in November 1977, said she plans to reintroduce the measure early in the new session of the council.

Mason said she believes the issue "has been made much more emotional and much more political than it should have been. It's still a civil rights issue."

Mason, who said her father was an adopted child who searched for his birth parents all his life and never found them, believes she has a lot of support among District residents.

She said that shortly after the bill was defeated last month, "People stopped me... and said, 'Aren't you Hilda Mason? It's too bad you lost the adoption bill.'"

The legislation, as it was originally introduced by Mason, would have allowed adoptees access to their records when they reached 18. District of Columbia adoption records now are sealed, as are the records in all but six states, and can be opened only when a court decides that the action will "promote or protect" the welfare of the adopted child. The six states that have open adoption record legislation are Virginia, Alabama, Connecticut, Kansas, Minnesota and Ohio.

Changes made in the bill by the judiciary committee and by council members last month added requirements that adoptees be 21 before they can request that records be opened, and that they attempt to obtain the consent of both their birth parents and their adoptive parents.

The waiting period for obtaining consent from both sets of parents was set at six months; if parents do not reply within another 45 days after the six-month period is over, the records would be opened.

Mason is expected to reintroduce the bill early in the new council session that began Tuesday, according to her legislative assistant, Chris Lipscombe.

She will present the legislation with most of the changes made by the judiciary committee and with amendments made during council sessions in November, Lipscombe said. He added that she does not plan to keep the amendment that would require consent from adoptive parents. He said the other provisions appear to "make up a reasonable compromise on the legislation."

After the bill is reintroduced, it must be referred to the judiciary committee, which can incorporate testimony from hearings on the legislation last spring rather than hold new hearings.

The legislation could come before the council for a vote in February or March, said Lipscombe.

Proponents of opening adoption records have attacked restrictions placed on the bill in November and are particularly bitter about the amendment requiring consent from the adoptive parents.

Joseph P. Saba, an attorney and member of Adoptees In Search, an organization of adult adoptees, said the provision requiring adoptive parents' consent for opening records "is to treat an adult adoptee as a mental incompetent. We are not possessions of our parents." He suggested that the amendment may be unconstitutional.

He said he believes that many backers of open adoption records would rather have no legislation at all than a law requiring parental consent from adoptive parents.

If the bill is passed early this year, implementation probably would start next October, according to Betty Queen, deputy chief of the Bureau of Family Services, a part of the Social Rehabilitation Administration.

"We would have to look at internal reviews and resources" to see how soon requests to have records opened could be taken from adoptees, she said, and added that "we would have to have waiting lists to start working" on the requests.

Queen said that a study in her department resulted in a finding that three social workers, an investigator and a clerical staffer would be needed to implement the legislation, and that the cost for these staff members would be about $65,000 annually.