Baghdad ? Kurdish lawmakers agreed Wednesday to a six-month delay in a referendum on whether the oil-rich city of Kirkuk should join the semiautonomous region of Kurdistan or remain under Iraqi central government control.

The delay had been expected because of problems in arranging logistics for the vote, which was supposed to have been held by the end of the year. A census to determine who would be eligible to vote, for instance, has not yet been done. But by putting off the issue, the lawmakers highlighted what has become a constant in Iraq: the inability of leaders to settle disputes whose resolutions are considered key to ending ethnic and sectarian strife.

Another major issue, the rewriting of the Iraqi constitution, also is unlikely to be completed by a Monday deadline. The head of the Iraqi parliament’s constitutional review committee, Humam Hamoudi, said Wednesday he would request a three-month delay. That would mark the fourth time the target date for revision of the document, approved in a referendum in 2005, has been put off as lawmakers haggle over such issues as provincial powers and religious and cultural freedoms.

The delay in the constitutional revision could hinder progress on other issues that the U.S. has cited as keys to Iraqi national reconciliation. Those include legislation to manage Iraq’s oil industry, and the scheduling of provincial elections to ensure better distribution of power among Shiite Muslims and Sunnis across the country. Both issues are tied to constitutional revisions that would spell out the powers of regional governments to manage oil and other resources; and establish what power provinces will have to manage their own affairs.

U.S. officials worry that without political progress, recent security gains will not be sustained.

Of the 111 lawmakers in the Kurdistan regional parliament, 94 voted in favor of postponing the Kirkuk referendum. The decision came at the advice of Staffan de Mistura, the United Nations’ special representative in Iraq.

While the delay had been seen by many as inevitable, legislators accepted it grudgingly. Sardar Harki, a member of parliament in Irbil, the Kurdistan capital, said the Iraqi government as well as Kurdistan leaders “should exert more efforts … to get this issue over and done with.”

A parliament member who opposed the delay, Ghafour Makhmouri, said he does not trust the Iraqi government to organize the referendum “in six months, nor in the future.”