The Interstate Commerce Commission found yesterday that the Chicago and North Western Transportation Co.'s proposal to purchase the bankrupt Milwaukee Road is "in the public interest," but said, on a 4-to-3 vote, it prefers the Soo Line Railroad Co.'s offer.

The decision is but another step in sorting out the chaotic Midwestern railroad scene. It sets the stage for a decision by the federal bankruptcy court in Chicago on who gets to operate what is left of the Milwaukee. The court could choose the CNW, the Soo or, theoretically, some other railroad.

A four-member commission ruled in September that the Soo offer was in the public interest, but was unable to reach a finding on the CNW. Since then, the CNW has amended its offer and three new members have been confirmed for the ICC, bringing it to seven members.

As a result, the bankruptcy court asked the commission to reconsider the CNW proposal. The CNW has offered about $210 million for the Milwaukee; the Soo about $172 million. However, the major issues for the ICC are not price but such questions as which midwestern railroad shall have the right to operate over which other railroad's track, and what employe protection provisions shall apply.

The commission spent most of a sometimes fractious session deciding more than 40 such issues. But its decision on a key question was unanimous: if the CNW gets the Milwaukee, the Soo Line will have the right to operate its trains over the CNW's so-called "spine line" between Kansas City and Northfield, Minn.

One of the more interesting issues was whether the Burlington Northern should have operating rights to carry coal on CNW-acquired Milwaukee track to three power plants. That question was undecided as the commissioners split 3 to 3, pending Commissioner Frederic N. Andre's vote. Without the rights, the Burlington would have to negotiate a joint rate with the CNW. The joint rate probably would always be higher than a single-line rate CNW could offer for the coal, Commission Chairman Reese H. Taylor Jr. argued.