Alaska Northwest Properties Inc., a subsidiary of Alaska Airlines that was spun off last week after it acquired a significant stake in Wien Air Alaska, yesterday told the Civil Aeronautics Board it is not under the agency's jurisdiction and would not file reports requested by it.

The board on Monday tentatively found that the subsidiary's stock interest was acquired illegally and that the takeover posed serious competitive problems.

The board gave Alaska and the subsidiary four days in which to convince the board the law was not violated and that the subsidiary's holdings should not be reduced to less than a 10 percent stake of Wien. As of Monday, it had a 28.3 percent interest.

In the meantime, both Alaska and Alaska Northwest Properties were ordered to file daily reports with the CAB outlining the preceding day's events and transactions.

Yesterday, Alaska Airlines filed a report but the subsidiary and Ronald Cosgrave, who became its chairman and chief executive officer last week when he resigned the same posts of Alaska Airlines, told the board they were not required to file the reports on grounds that the CAB lacked jurisdiction.

Reuben B. Robertson, director of the CAB'S Bureau of Consumer Protection, said last night the board had not taken any action to compel production of the reports. He added that a U.S. District Court in Seattle would be holding a hearing on the issues raised by the takeover -- Household Finance Corp. is also a bidder -- at which the CAB would be intervening.