The Democratic Party yesterday carried out the first phase of its threat to punish Minnesota and South Dakota for scheduling their delegates to be selected two weeks earlier than party rules allow. By a resolution passed unanimously by the party's rules committee, Minnesota was stripped of six of its 86 delegates and South Dakota of four of its 19 delegates to the 1988 national convention. Those delegate seats had been set aside for Democratic National Committee members from those states. The complete DNC is expected to give final approval today.

The party rejected one element of the plan aimed at penalizing Minnesota, turning down a proposal to deny a delegate's seat to Walter F. Mondale, the party's 1984 presidential nominee.

Minnesotan Mark Dayton, a department store heir and former Senate nominee, withdrew a $100,000 pledge to the DNC because of its stance on his state's primary.

The two states also were barred from participating yesterday in selecting hotel rooms and convention floor space. They will have to settle for what is left after the other states and jurisdictions make their choices.

Kathy Vick, chairman of the Compliance Assistance Commission, said making an exception for the two states would be unfair to others who persuaded their legislatures or parties to change dates to comply with the rules.