American businessman Francis J. Crawford pleaded innocent in Moscow City Court yesterday to a charge of black market currency dealings and put up a vigorous defense. He said the Soviet secret police misunderstand their own country's money exchange rules, and he repeatedly challenged prosecution witnesses on key points of their testimony.

The 37-year-old native of Mobile, Ala., wearing his customary cowboy boots - a conservative black - and a carefully tailored gray suit, denied the prosecution charge that he bought 20,000 rubles for $8,300, nearly four times the official rate, in dealings with one of three Soviet codefendants.

"I have exchanged no dollars except through the Soviet Bank for Foreign Trade," the only legal exchange method here, he told state prosecutor Mikhail Ilyukhin.

In contrast to the trials of Soviet dissidents, Western reporters and American officials were admitted to the courtroom.

Crawford, products manager in Moscow for International Harvester, was dragged from his car June 12 by Soviet police and charged with criminal currency violations, which carry a maximum eight-year sentence in a labor camp.

The unprecedented case against a resident American business representative here is widely viewed as Kremlin retaliation for the arrest of two Soviet employes of the United Nations on charges of naval espionage. They are scheduled to go to trial in New Jersey Sept. 12.

Crawford's three Soviet codefendants, who all face stiffer charges, pleaded guilty at the opening of the trial yesterday and then testified against Crawford or each other.

The trial began promptly at 9 a.m. with the Soviet defendants, Vladimir and Lyudmila Kiselyov, and Alla Solovyov, sitting between prison guards in a dock across from the prosecutor.

Crawford sat in the audience in the front row, with two International Harvester lawyers, three U.S. Embassy officials and his fiance, Virginia Olbrish, an Embassy secretary. Six Western reporters were allowed inside the court, but another two dozen correspondents were barred, and the 20 other seats in the small first-floor room were occupied by "official observers."

Soviet accusations at the trial yesterday centered on testimony by Kiselyov of numerous illegal currency deals with Crawford dating back to early last year and prosecution assertions that the Harvester Moscow office spent far more rubles than were exchanged officially, implying Crawford paid company bills with black market rubles he got from Kiselyov.

Kiseljov had been convicted previously of currency violations and faces a possible death sentence in this case.

Kiselyov, 40, makes only 120 rubles a month as a factory checker, but has allegedly accumulated more than 13,000 rubles in black market deals in the past years. He said he usually met Crawford outside the Harvester office on Pokrovsky Boulevard in central Moscow.

"Crawford demanded that we must be very very careful and take special precautions," he testified. He told of illegal currency deals with an Italian, and Ecuadorian diplomat, a West German and several Afghanis. All these persons, some students, some diplomats, some businessmen, have been expelled by the Soviets sinc the KGB secret police began their investigation of Kiselyov last spring.

Crawford specifically denied any currency transactions with Kiselyov, but recounted various visits to the man's wife, a seamstress, for mending or alterations. He maintained he gave her only small gifts in return, such as toothpaste, and once, a Stetson hat he brought from United States. He told Judge Lev Mironov he never paid money of any kind to the couple or discussed illegal purchase of rubles.

Kiselyov read his entire testimony and declined to personally cross-examine Crawford. Crawford, who speaks little Russian, asked through his translator why Kiselyov had read his account if he were so sure of his facts. The accuser replied it was because he had had "many clients," to laughter from the audience.

Mrs. Kiselyov asked several questions of Crawford, then abruptly asked, "Why don't you admit your guilt?" Crawford replied coolly: "If you commit no crime, you certainly do not say you do."

She alleged that Crawford last Dec. 23 sought to sell the Kiselyovs $1,000 at inflated black market ruble rates. But Crawford rebutted, saying he was in the United States from Dec. 21 through Jan. 27.

Crawford, also charged with illegal dollar purchase of six antique samovars, denied buying them, saying he could get them much more cheaply - and legally - at special state secondhand stores.

When Prosecutor Ilyukhin asserted that Soviet bank records showed Crawford had withdrawn no rubles during all of 1978 with which to pay office bills, Crawford produced copies of an officially stamped from requesting 4,000 rubles from the bank in February in Harvester's name. He gave photocopies to the judge and Ilyukhin.

Ilyuknin said bills paid by Harvester exceeded the amount of rubles Crawford had drawn from the bank anyway. Crawford explained at length that Soviet practice is to charge resident Americans in rubles for such services as rent, utilities and communications, and require payment in dollars by bank transfer that does not show up as a ruble transaction.

After court, Crawford said the case comes down to a "misinterpretation of Harvester expense records and accounts" by the Soviets.

The Soviets spiced up the trial by bringing in as a prosecution witness Larissa Formanova, a bleached blonde in a long black cocktail dress and dyed fur cape. She told reporters outside the courtroom she was a secretary and then testified she had had "a personal relationship" with Crawford. She said she had originally introduced Crawford to Kiselyov, because Crawford allegedly "wanted to buy rubles and not at the bank."

Questioned by Crawford, she repeated that she had met him in room 1821 of the Intourist hotel early last year. But at the time, he said, he was staying in room 1120 and did not begin living in 1821 until late last year.

The Soviet news agency Tass last night said Crawford "avoided recognizing his guilt," said added that Kiselyov's testimony showed that "initiative for the illegal deals came from Crawford, who practically played the main role in their criminal relationship."

Crawford and his American lawyers, Harvester assistant general counsel Robert Booth and Peter Maggs, a law professor, reportedly are certain Crawford will be convicted regardless of his defense efforts in what they see as a purely political - not a judicial - trial. But emotions ran high after Crawford left the courtroom. U.S. consular official Robert Pringle shook his hand warmly and declared his defense to have been "magnificent?"

The trial continues today.