The two sides were trying to set a specific date at high-level talks in Seoul for starting service on the 25-kilometer-long (16-mile-long) track running to a joint industrial complex in the North's border city of Kaesong, Unification Ministry spokesman Kim Nam-shik said.
"Both sides shared an understanding that it would be meaningful in further vitalizing the Kaesong industrial complex," Kim said.
In May, the sides conducted a one-time test run on the track and another reconnected rail line, marking the first train crossings of the frontier in more than half a century. But no regular service has yet started.
This week's talks between the prime ministers of the two sides - the first such meeting in 15 years - are aimed at fleshing out the summit accord that calls for greater peace and economic cooperation between the two sides.
Also on the agenda for the three days of meetings running through Friday are the South's offers to repair a major North Korean road and a railway, build two shipyards there and provide medical assistance for the impoverished nation.
The two sides held working-level sessions on the construction and medical projects on Thursday in a "buisnesslike atmosphere," said the spokesman Kim, without giving any details.
He said the sides were also close to agreement on setting up a joint task force to carry out an agreement to turn the area around their disputed western sea border into a "peace and cooperation zone" by establishing a joint fishing area and building a special economic zone nearby.
Earlier Thursday, South Korean Prime Minister Han Duck-soo and his North Korean counterpart Kim Yong Il strolled through a Seoul hotel but did not meet for formal talks, leaving technical discussions to lower-level officials.
At the start of the talks Wednesday, both Han and Kim called for quickly implementing the summit agreement, praising it as a big step toward reconciliation and peace on the divided peninsula.
The high-level talks come amid progress in international efforts to rid North Korea of its nuclear programs, with the communist nation recently beginning to disable its sole operational nuclear reactor under a deal with the U.S., South Korea, China, Japan and Russia.
U.S. nuclear envoy Christopher Hill and Mohamed ElBaradei, head of the International Atomic Energy Agency, met in Austria on Wednesday to discuss how to make further progress in North Korea's denuclearization.