The D.C. City Council last night gave preliminary approval to a bill that would give it the authority to offer amendments to the proposed statehood constitution, a move some supporters of the document say may improve its chances for passage in the Nov. 2 general election.

The council's action came amid new indications that many city leaders who oppose some sections of the constitution believe it should be passed to avoid sending the constitution back to the statehood convention for possible revision.

The officials, including representatives of the mayor's office, the statehood movement and organized labor, say privately that the statehood convention's 45 delegates are too disorganized and politically insensitive to write a document that can win Congress' approval.

"It would be better for the constitution to be handled by the council and Congress now," said one critic of the convention after the City Council's regularly scheduled night session.

Any amendments made to the constitution, including any that might be made by Congress, after its approval by voters would have to be submitted to the voters for ratification.

D.C. Delegate Walter Fauntroy, who previously has declined to endorse the constitution, is expected to hold a press conference today to urge voters to approve the document, but with the understanding its controversial sections can be reworked by the council or Congress.

The Metropolitan Washington Council, AFL-CIO, endorsed the document Monday night, but labor officials said privately yesterday that the document needs significant revisions.

Mayor Marion Barry has said he will vote for the constitution, but a top aide to Barry said the document is seriously flawed and should be amended by the council.

Joel Garner, a convention delegate who supports statehood but has urged the constitution's rejection, said last night that the council's action will only confuse the voters.

"What they are saying is, 'If you're against it, vote for it,' " Garner said. He said the convention would be under pressure to revise the document if it is voted down.

The council scheduled a final vote on the measure Nov. 16, after the election. The bill, sponsored by Hilda Mason (Statehood-At Large), was approved by a 7-to-4 vote with one abstention.

Mason said the council's vote signaled its willingness to address concerns raised by those who have questions about parts of the constitution. Critics have pointed to several, including provisions that could allow police and firefighters to strike and could guarantee all city residents a job or adequate income.

The council's action would amend the statehood initiative approved by the voters in 1980. By law, initiatives are subject to the same amendment process as other city laws.

Voting with Mason were Council Chairman Arrington Dixon, Charlene Drew Jarvis (D-Ward 4), Wilhelmina J. Rolark (D-Ward 8), William R. Spaulding (D-Ward 5), David A. Clarke (D-Ward 1) and Nadine P. Winter (D-Ward 6). Voting against were Betty Ann Kane (D-At Large), H. R. Crawford (D-Ward 7), John Ray (D-At Large) and Polly Shackleton (D-Ward 3). John A. Wilson (D-Ward 2) abstained. Jerry A. Moore (R-At Large) was out of town yesterday.

In other action, the council rejected a move by Crawford to require parents to accompany children under 12 on Halloween night trick-or-treating. Several members said the measure was unenforceable.

The council enacted a law, proposed by Clarke, that outlaws the wearing of masks by anyone trying to infringe on the civil rights of others. The law, modeled after several state laws, is aimed at a Ku Klux Klan group that has expressed an interest in holding a march in Washington next month.