A Superior Court judge refused to overturn the 1972 firebombing and conspiracy convictions of the Wilmington 10 here today, ruling that the civil rights activists got a fair trail five years ago.

The defense case was crippled toward the end of a post-conviction hearing when a star prosecution witness, who had recanted his 1972 testimony, retracted his recantation.

Judge George M. Fountain concluded abruptly after listening to two weeks of testimony in the case that there had been "no substantial denial of any constitutional rights of the defendants."

His ruling touched off a small demonstration on the sandy lawn of the Pender County Courthouse here and prompted bitter words from defense lawyers for the Rev. Benjamin F. Chavis, who is serving a prison term of up to 34 years as the leader of the Wilmington 10.

"My reaction is that a great injustice has been done," commented chief defense lawyer James E. Ferguson II of Charlotte. "This decision represents a certain callousness of the issues we've raised."

One issue Ferguson raised was that state prosecutors badgered, coached and bribed witnesses to lie against Chavis, eight high school blacks and the white poverty worker who were sent to prison for the night firebombing of Mike's Grocery in coastal Wilmington, N.C., during 1971 racial unrest.

But, the Foreign Communist press quickly seized upon the re-hearing and the case as an example of the stifling of "human rights" in the United States.

Activist Angela Davis led protests in Paris earlier this month. Soviet reporters traveled to North Carolina to interview Chavis in his jail cell and a camera crew from East Germany scrambled for close-ups of shackled, black inmates testifying here.

Although the U.S. Supreme Court refused to hear an appeal in the case more than a year ago, defense attorneys, including John P. Redmond of New York Gov. Hugh Careys law firm. Manning, Carey & Redmond argued that recantations by prosecution witnesses revealed evidence of official misconduct at the original trial.

In a surprise twist Monday, though, one former chief witness, Allen Ray Hall, 12, withdrew his recantation in a tape-recorded phone call to prosecutor James T. Stroud, the very man defense attorneys had accused of extracting perjury in 1972 in return for light sentences and other favors.

On Thursday, a weary defense disclosed it had its own tapes of Hall affirming his recantation. The roly-poly convict insisted that he'd lied to Stroud. "I swear to Allah . . . it was not true," he said.

The farmer folk of Burgaw paid little attention to the proceedings in their magnolia-shaded courthouse, but state Attorney General Rufus Edmisten, an aide to former Sen. Sam J. Ervin Jr. during the Senate Watergate hearings, recently stepped up his criticism of the defense effort.

In a Winston-Salem interview last week he called the recantating witnesses "a bunch of brazen liars."

"Ever since the first trial," he said, "they've told us 17 different versions, 17 different recantations."

But to staunch Wilmington 10 supporters, like Charles Cobb, who directs the United Church of Christ-fund Commission for Racial Justice, which has poured $500,000 into the cause, the state has put itself in an embarassing position by challenging the creibility of its own former witnesses.

"If they're lying now," he muttered in the tightly guarded courtroom one day last week, "what were they doing in 1972?"

Chavis, a native of Oxford, N.C., worked for the Commission for Racial Justice in Washington until he began serving his sentence in 1976.

Judge Fountain contended that the post-conviction hearing was not to determine the guilt or innocence of the defendants, who were convicted here originally by a jury of 10 whites and two blacks.

The defense plans to appeal his decision and to continue its support of a habeas corpus petition that could eventually lead to a federal court hearing on the convictions.

Still uncertain is the Justice Department's future role in the case, which was investigated by the FBI on direct orders from Attorney General Griffin B. Bell, who received considerable podding from the Congressional Black Caucus.