Appointed Sen. Muriel Humphrey will get her first test as a possible candidate tonight at 4,000 precinct caucuses, and some democratic leaders predicted an outpouring of support for her to become the elected successor to her late husband, Hubert.

Abortion and administration farm policies are expected to be the prime issues at the neighbourhood caucuses of both parties. The caucuses are the first step toward formal endorsement and platform adoption at state conventions in June. Rick Scott, state Democratic chairman, predicted yesterday a surprising surge of demand for higher farm prices, specifically for full parity.

Humphrey, who was appointed by Gov. Rudy Perpich to serve until the November election, is delaying, until perhaps as late as April, a decision on whether to run for the remaining four years of her late husband's term.

She will be in Washington during the caucuses here, and hasn't campaigned for backing. She was urged to run for election by Minnesota AFLCIO executive council, a strong influence in the Democratic Farmer Labor Party, as it is officially called in Minnesota. And if she does run she already has widespread pledges of support from her late husband's friends and associates.

Rep. Don Fraser, who has announced that he'll run for the Senate seat regardless of the Humphrey decision is asking her supporters at the Democratic caucuses to give him their "next choice" support. He is a leader of the liberal wing, and an opponent of efforts to ban federal funding for abortion.

Nicholas Coleman, the state Senate's Democratic leader, plans to run if Humphrey doesn't, and is trying to stake out a middle abortion position.

The anti-abortion leaders haven't confronted Humphrey, who told a recent news conference that she supported the 1973 Supreme Court abortion decision and favored government funds for indigent women who want abortions.

The expected strategy by the anti-abortion group, which has flooded the state with literature, is to elect delegates who, if Humphrey doesn't run, could support an anti-abortion candidate.