Ministers want to wait until next year before consulting on the future of civil partnerships.
Government lawyers told the Supreme Court the wait was "justified" so four whole years of data could be gathered following the introduction of same-sex marriage.
The court is hearing the case of Rebecca Steinfeld (37) and Charles Keidan (41), who want a civil partnership but are prevented by legislation which says only same-sex couples are eligible.
The academics, who live in west London, suffered defeat at the Court of Appeal in February last year, but were given the go-ahead in August for a Supreme Court hearing.
A panel of five Supreme Court justices, including court president Lady Hale, began considering the couple's appeal yesterday.
James Eadie QC, representing the equalities minister, told the court the Government wants to wait until September next year before it considers what to do and would launch a public consultation. He said civil partnerships are "essentially identical" to civil marriage and were created to give legal recognition to same-sex unions at a time "when society was not felt ready" to recognise such relationships as marriages.
Mr Eadie told the judges it is accepted Ms Steinfeld and Mr Keidan have a "genuinely held" objection to marriage, but the Government's decision to "take some time" before deciding on the future of civil partnerships is "justified". He said: "These are highly sensitive social (and indeed political) issues in which the Government and Parliament are currently, actively and seriously engaged on a defined timescale and process.
"The process has taken some time - a fact that is in part due to an understandable and legitimate concern to gauge the reaction over a period of time to the introduction of the Marriage Act 2013."
He later added: "The future of civil partnerships raises difficult questions of social policy for which there is no obvious answer and Parliament has a Bill before it with different options to deal with those difficulties."