SEOUL, Nov. 16 (Yonhap) -- The main opposition Democratic Party decided Wednesday to reject President Lee Myung-bak's offer to demand renegotiation on a key clause of the free trade agreement with the United States if the deal is ratified first, its spokesman said.

The decision is expected to further delay the ratification process.

In a bid to break a prolonged standoff, Lee made a rare visit to the National Assembly Tuesday and promised leaders of rival parties that the government will ask for a renegotiation on the investor-state settlement, known as the ISD, with American counterparts within three months after the FTA goes into effect.

On Wednesday, DP lawmakers held a lengthy meeting on the proposal and decided to stick to their existing position that the government should first scrap the ISD provision before ratifying the agreement.

"President Lee's oral promise is not enough to change the party's official position," DP spokesman Lee Yong-sup said. "We want the written agreement made between ministerial-level officials of the two countries with promises to scrap the ISD clause."

In Washington, the U.S. government supported Lee's offer. An American trade official, who wished to remain anonymous, told Yonhap News that Washington is willing to discuss the ISD issue once the deal takes effect.

Earlier in the day, DP leader Sohn Hak-kyu, a hard-liner, reiterated his position that the government should first renegotiate with the American counterparts to scrap the ISD provision before ratifying the accord.

"I have not changed my basic stance that (the parliament) should not hurriedly pass the (ratification) bill," Sohn said in a senior party meeting.

DP floor leader Kim Jin-pyo made the similar point, saying that Lee's offer is "insufficient and disappointing," considering the DP's demand to scrap the ISD clause from the agreement before approval.

Some lawmakers, who conditionally favor the deal, said the party should accept the new offer to avoid a prolonged standoff.

"Though insufficient, Lee's offer was a step forward," the party secretary general Jeong Jang-seon said.

Jeong was one of 45 DP lawmakers out of 87 who signed a compromise plan last week that promised not to physically block the ratification process if the government agrees to renegotiate the ISD provision after ratification.

After the U.S. Congress approved it last month, the government and ruling Grand National Party (GNP) came under pressure to speed up the ratification process to make the deal go into effect on Jan.

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The GNP, which holds a comfortable majority in the 299-member unicameral parliament, has been reluctant to railroad the bill to avoid a deadlock that could further anger voters fed up with the partisan gridlock that has plagued major legislations.

The GNP vowed to make more efforts to pass the trade pact as soon as possible with a new offer on the controversial provisions, which have stymied the legislative process.

"Regardless of any hurdles, (the GNP) will pass the S.Korea-U.S. FTA by all means," party leader Hong Joon-pyo said during a lecture. He stopped short of saying how and exactly when that goal would be accomplished. "I believe that the political parties will negotiate to reach an agreement to pass the deal."