The prime ministers of North and South Korea announced a significant package of cross-border economic projects today to help rebuild the North’s broken economy and ease military tension on the divided Korean Peninsula by increasing human and cargo traffic across the demilitarized zone. At the end of three days of talks here, North Korea’s prime minister, Kim Yong-il, and his South Korean counterpart, Han Duck-soo, agreed to start cross-border freight-train service for the first time in more than half a century, scheduling the first, and highly symbolic, border crossing a week before South Korea holds presidential elections on Dec. 19.

Then, starting in the first half of 2008, fishing boats from the two Koreas will work together in a joint fishing zone in the same frontier waters where their respective navies engaged in a bloody skirmish in 2002, the prime ministers said.

Also, the North will relocate its warships from Haeju, a naval base near the border, to make room for South Korean cargo ships and a new industrial complex to be built there by South Korean investors. Construction will begin as early as next year.

“These projects will chip away at the DMZ,” said Koh Yu-hwan, an expert on North Korea at Dongguk University in Seoul. “They are steppingstones toward what we hope will become a confederation of the two Koreas before eventual reunification.”

The joint economic projects will cost South Korea between $11.1 billion and $15.8 billion, according to Kim Young-yoon, a researcher at the government-run Korea Institute for National Unification.

The two government leaders have huddled in Seoul since Wednesday to advance the rapprochement created by the inter-Korean summit meeting in early October and the North’s decision to disable its nuclear weapons facilities.

At the October meeting, President Roh Moo-hyun and the North Korean leader, Kim Jong-il, called for negotiations on a peace treaty that would formally end the state of war between their countries.

The meeting this week was free from the kind of haggling common in inter-Korean negotiations. Analysts said the two sides were bonded by a common desire to influence the December presidential election by strengthening South Korean liberals, who favor reconciliation and investment for the impoverished North.

For North Korea, the talks this week provided a last opportunity to win major investment commitments from the South before Mr. Roh’s liberal government steps down in February.

Mr. Roh is barred by the Constitution from running. But liberal candidates close to him are lagging behind the conservative candidate, Lee Myung-bak, by large margins.

Some analysts noted that the meeting was notable for avoiding direct discussion of North Korea’s nuclear weapons, the focus of international sanctions. The South believes that investments will help the government in the North see the long-term benefits of giving up nuclear weapons.

“It is really disappointing to the international community that the prime ministers of the two Koreas meet for the first time in 15 years, but their agreements didn’t raise a peep about North Korea’s nuclear weapons programs, a major international security threat,” said Nam Joo-hong, a North Korea expert at Kyonggi University.

The two sides said freight trains would begin regular service on Dec. 11 on a 16-mile track linking the South Korean city of Munsan and a joint industrial complex in Kaesong , a town just north of the border.

Trucks and buses already run between the towns on a newly built road. But train service, even if a short distance, marks a significant first step in South Korea’s grand design: connecting its railways to China, Russia and Europe, its three fast-growing export markets.

As part of that dream, South Korea also agreed today to repair North Korea’s decrepit railroad all the way between Kaesong and the North Korean border with China, starting next year. It will also start building shipyards in North Korea next year.

“I firmly believe that today’s agreement will contribute greatly to bringing peace and prosperity on the Korean Peninsula,” said Unification Minister Lee Jae-joung, South Korea’s main policymaker on the North.

The new projects will lift South Korea’s competitiveness as it vies with low-cost China in the global marketplace, officials said.

The South is already the North’s No. 2 trading partner, behind China. Trade between the Koreas surged 23 percent to $1.4 billion in the first 10 months of this year. About a quarter of the trade came from goods produced at Kaesong , where 20,000 North Korean workers produce garments and kitchen utensils at 50 South Korean factories, earning only one-third of what their Chinese counterparts do.

Goods from Kaesong were excluded from a free trade agreement reached in April between South Korea and the United States amid fears in Washington that projects like Kaesong could buttress the North Korean government before it abandons nuclear weapons.

South Korea’s decision to create another such industrial complex at Haeju, near Kaesong , could further complicate the prospects of United States congressional approval of the trade agreement, Mr. Nam said.

South Korea agreed today to expand the Kaesong complex. The North said it would allow South Koreans to use the Internet and cellphones inside Kaesong ; they are forbidden in the rest of the isolated country.