A federal judge in Alexandria dismissed a bribery charge yesterday against Dr. Murdock Head, founder and longtime executive director of the Warrenton-based Airlie Foundation.

Head was convicted last year of participating in a criminal conspiracy and was sentenced to three years' imprisonment.He is currently appealing his conviction on the single conspiracy count.

The separate bribery charge was dismissed by U.S. District Court Judge Oren R. Lewis, who acted at the prosecution's request. Prosecutors, however, reserved the right to pursue the bribery count agains Head if his conspiracy conviction is overturned by the appeals court.

The bribery count alleged that Head gave a $1,000 payoff to former congressman Daniel J. Flood in 1974. The count was temporarily set aside by Lewis last year and was not considered by the jury that convicted Head of conspiracy.

Flood, a Pennsylvania Democrat, pleaded guilty last month to a misdemenor charge of conspiring to solicit illegal campaign contributions and was placed on one year's probation. In exchange for the guilty plea, prosecutors agreed to dismiss more serious conspiracy, bribery and perjury charges against Flood.

Head was adquitted of two tax-evasion charges by the jury that convicted him of conspiracy last October. Lewis later dismissed a third tax-evasion count after the jury reported itself deadlocked on the charges. Lewis had previously dismissed eight other counts on which Head was indicted.