South Korean police placed about 270 opposition politicians under house arrest this morning and sealed off their party's headquarters in an effort to scuttle a campaign for constitutional revision, according to reports from Seoul.

Those under house arrest included Lee Min Woo, president of the opposition New Korea Democratic Party, and Kim Young Sam, a senior party figure. Kim Dae Jung, another opposition leader, remained confined under a house arrest imposed last week.

Interviewed by telephone, Lee called the government actions an "unprecedented outrage." About 100 policemen were reported deployed outside his home to prevent him from leaving.

The 270 persons confined today are members of the opposition party's central committee. More than 70 of them are also members of the National Assembly. It was not clear how long the restrictions would last.

They had planned to meet at party headquarters in downtown Seoul today to open formally a drive to collect signatures calling for immediate revision of the constitution to provide for direct election of the president.

They contend that the current electoral college system will allow President Chun Doo Hwan to manipulate the results and choose his successor in voting scheduled for 1988. Getting the change has become the opposition's main rallying point.

The government views the signature campaign as a challenge to its authority and responded last week with a wave of arrests, manhandling of politicians and office searches. It has suggested it will arrest anyone who signs or circulates the petition.

Early this morning, police entered the headquarters of the New Korea Democratic Party and carried away documents. About 300 police in riot gear blocked the entrance of the building.

Police began the crackdown last week after opposition politicians, foreseeing action against the meeting planned for today, began signing the petititions at two separate gatherings. So far, about 220 signatures have been collected.

Police responded by sealing off party headquarters and the office of another opposition-affiliated group, the Council for Promotion of Democracy, and reportedly roughing up opposition leaders. They also dragged Korean reporters covering the event down flights of stairs.

One hundred one opposition politicians are reported to have been detained and interrogated since last week, in addition to today's house arrests. All but about a dozen of those have been released.

Last week, South Korean police raided 110 college and vocational school campuses. On Feb. 4, they arrested 252 students at demonstrations. About 205 of them are still being held, according to reports from Seoul.