Kim Dae Jung, South Korea's veteran opposition leader, strongly indicated today that he will launch a new political party that presumably would be the vehicle for his presidential candidacy next year.

Kim, who is in a running feud with many in the main opposition movement, the New Democratic Party, said he will delay a decision until the country's new political rules become clear. He said he will concentrate now on a new, non-partisan movement constructed to keep pressure on the interim government for a new constitution and other democratic reforms.

But Kim strongly suggested in an interview that the movement may be transformed into a new opposition party to campaign in a presidential election hoped for next year.

"As this movement proceeds and some progress is made, why should we not consider having a new party?" he asked.

Meanwhile, about 6,000 students held rallies for the second day here to demand democratic reforms and an end to marial law. Speaking at the National Assembly, Prime Minister Shim Hyon Hwak said today that maritial law will be lifted before next year's presidential election, a statement that seems to contradict Tuesday's assertion by the key military commander, Lt. Gen. Chun Doo Hwan, that this would be done only after "proper conditions are created.

Kim's hints of forming his own party have discouraged many opposition leaders who see the split in their ranks as aiding only the government. Former president Yun Po Sun and other prominent dissidents have tried to discourage him.

But the dispute between Kim and Kim Young Sam, current New Democratic Party president, has become increasingly bitter, with party trying to expel some of Kim Dae Jung's followers.

Kim Dae Jung bolted the party recently following confrontations that eruptued in fistfights when he charged that the majority faction prevented his followers from being elected to certain party posts. Both Kims want to run for president, and the exclusion of Kim Dae Jung's loyalists lessened his chances of getting the party's nomination.

The feud, which was widely publicized in Seoul's censored press, is seen as a great boon for whomever the interim government decides to back, something that remains in question. The former government's vehicle, the Democrat Republican Party, is headed by Kim Jong Pil, who also wants to run for president but is said to be opposed by the military faction that now wields considerable power in the civilian government.

That military fraction has made no secret of its hostility to Kim Dae Jung, who came close to defeating President Park Chung Hee in 1971 and who subsequently spent 33 months in prison for violating one of Park's emergency decrees.

The military has censured him indirectly for speaking on a college campus, implying he was stirring up rebellious students, and has spread the word he is considered a radical. Kim Dae Jung's backers also report a strange inability to rent office space for a political headquarters, and several building owners have returned money paid on rental contracts saying only that they want to get out of the agreements.

Kim's current strategy is to form what he calls a "Pan-National Movement for Democratization," with such political goals as freeing remaining political prisoners, ending martial law, amending the constitution and calling elections. The government has hinted generally at holding a constitutional referendum this fall and elections next spring, but no timetable has been announced.