South Korea's new martial law rulers appear to have broken the late president Park Chung Hee's record for number of jailed political opponents and are expected to keep them in detention at least until an October referendum on a new constitution, according to dissident sources here.

Figures compiled by relatives of the jailed political figures and opposition militants indicate more than 700 are being held here and another 500 in the southern city of Kwangji, scene of a mass insurrection after the May 17 national martial law decree. About 600 opponents of the Park government at most were in jail at one time in the early 1970s, in the wake of his assumption of one-man control of the country.

The most prominent dissident now in jail, Kim Dae Jung, was Park's opponent in the 1971 presidential election. Kim was later jailed by Park, then released in 1978. He was jailed again May 17, and foreign diplomats say an anticipated government attempt to try him for sedition, a capital offense, could spark more antigovernment activities. Kim is from the Kwangji area and prosecutors are expected to argue that he had contact with leaders of the insurrection.

Kim's family is reportedly now under a form of house arrest, but wives of other jailed opponents are actively petitioning for their release, with no results so far. "During the Park time we knew what to do and how to fight; we knew what the target was," said Park Young Gil, whose husband, Presbyterian minister Moon Ik Hwan, is in prison for the third time.

"But now we don't know what to do. The military has everything. We don't know where to go or whom to petition."

Moon was arrested shortly before midnight May 17, the same time that Kim and hundreds of other outspoken opponents of military rule were rounded up in Seoul. Moon's wife said martial law command investigators in civilian clothes entered the house "without even taking off their shoes," the polite Korean custom. They told everyone to keep still, searched the house and then led Moon off, his wife said.

Reports have circulated here from a few detainees who have been released that most are being held at a former Korean Central Intelligence Agency compound on South Hill near downtown Seoul.

In the past, younger and less well-known opponents of the government have sometimes been beaten while in detention, but prominent prisoners like Kim or Moon have not been physically abused.

"Many of us are worried now, however, because this is the Army arresting people and they are rougher," said one woman whose husband, an academic who has opposed martial law rule, has gone into hiding with hundreds of other dissidents. "Soldiers just play rougher, even with their own people," said a foreign diplomat. "If a trooper gets out of line, they beat the bejeezus out of him."

There are no confirmed reports of mistreatment of detainees in Seoul, although mistreatment of people in Kwangji by Army troops was one of the most important causes of the uprising there.

Park and Lee Jung Ok, the wife of another jailed Presbyterian minister, Lee Hae Dong, said in an interview that they each received a telephone call recently from a man who identified himself as a member of the Committee for National Security, an official group in charge of the detentions.

The man said their husbands were safe, fed three meals a day, were permitted to bathe and had clean clothing. He refused their requests to visit their husbands and said he could not disclose their locations because investigations were still proceeding.

Both men were jailed previously for illegal assembly in 1976 when they signed a joint statement with several others calling for restoration of democracy. Both have been openly critical of the military group, led by Lt. Gen. Chon Doo Hwan, which took control of the government after the assassination of Park Chung Hee in October.

Several dissident sources say officials have told them the jailed opponents make "too much noise" that might distract from a referendum to approve a new constitution by October. Many officials here expect opponents to remain in detention at least until then, or until new assembly and presidential elections next year or even longer. Martial law commander Lee Hui Sung sought to assure several Christian leaders here last week, however, that jailed ministers would not be harmed.

With all public dissent outlawed, unlike the relatively free months following the Park assassination, some opponents are reported to be contemplating terrorist activities, such as kidnapings. But most seem unlikely to join demonstrations like those that rocked Seoul before May 17."Before they thought they had a chance to influence things," said one foreign observer, "but not now."