The U.S. Court of Appeals here refused yesterday to block a misconduct investigation of U.S. District Court Judge Alcee L. Hastings of Miami, but the court said it is too soon to rule on Hastings' contention that the investigation was unconstitutional.

The decision by a three-judge panel is the latest setback in Hastings' efforts to stop the probe, launched in 1983 by a committee of five judges after Hastings was acquitted of conspiracy to solicit a $150,000 bribe.

Washington lawyer William A. Borders, a codefendant, was found guilty in the case.

Terence J. Anderson, Hastings' lawyer, said he is "gratified" that the appeals court vacated a ruling by U.S. District Court Judge Gerhard A. Gesell. He had upheld the 1980 federal law giving the Judicial Conference, composed of chief judges of various federal courts, power to investigate and discipline sitting judges.

The appeals court said Gesell's ruling was "premature" because the investigative panel has taken no concrete action against Hastings.

In another decision, the appeals court panel dismissed a lawsuit challenging the legality of Reagan administration efforts to aid counterrevolutionaries fighting the Sandinista government of Nicaragua.

The court upheld a ruling in 1983 by U.S. District Court Judge Howard F. Corcoran that the suit by 12 members of Congress, 12 Nicaraguan citizens and two Florida residents dealt with political questions not subject to judicial decision.

In the Hastings decision, written by Circuit Judge Carl McGowan, the court said it would permit proceedings against Hastings "to unfold as they will" because of the general judicial principle that courts should not interfere with administrative actions until they have been completed.

Hastings had contended that the law permitting judges to discipline other judges -- through reprimand, censure or taking cases away from them -- was unconstitutional. He argued that federal judges, who have lifetime appointments, can be investigated and impeached only by Congress.

In a concurring opinion, Circuit Judge Harry T. Edwards declared that the law is unconstitutional although he said he agreed with McGowan that the case was not "ripe" for such a ruling.

"Our self-righteous finger-pointing at Judge Hastings may blind us to the reality that his case has more to do with the potential diminution of the independence of the judiciary," Edwards wrote, "than with the alleged misconduct of an individual judge . . . . "