The former executive vice president of Jefferson Bank and Trust Co., charged with obtaining a $25,000 loan from the Prince George's County bank by making the loan in the name of a fictitious person, had "no reason" to doubt that the person existed at the time the loan was approved, his defense lawyer told a federal court jury here today.

The former bank official, Thomas C. Pulliam Jr., who was fired from Jefferson last year after bank officials said they discovered that part of the loan went to him, will testify that he made the loan in part on the recommendation of a friend, Gordon R. Butler, a Northern Virginia private investigator who has become the government's chief witness against him, Pulliam's attorney said in his opening statement to the jury.

Whether Pulliam knew he was making the loan to a nonexistent person is likely to be a crucial and hotly debated issue at the trial. This and other testimony will provide an inside glimpse of the troubled Prince George's bank.

The three-count indictment against Pulliam charges him with conspiring with Butler to fraudulently obtain the $25,000 loan in May 1981 by using a fictitious name, "Robert L. Baker" and with submitting false financial information to get the loan.

The government contends that Pulliam used $10,000 from the $25,000 loan and $12,000 from an earlier loan he made to Butler in Butler's real name to help finance Pulliam's half interest in a satellite television antenna business he was starting with another bank customer.

Andre Michaud, Pulliam's partner in the antenna business and the operator of a video shop in Clinton, testified today that the partnership broke up in mid-1981 when Pulliam invested only $22,000 out of the $30,000 he had agreed to provide.

Michaud testified that on June 27, 1981, Pulliam and four other men, including "two large gentlemen," came to his store seeking the $22,000 Pulliam had invested and the satellite antennas Michaud had purchased.

When one of the men with Pulliam spotted the antennas locked in a back room, Pulliam asked for the room key, but Michaud refused, Michaud said under oath. Pulliam then turned to one of the other men and said "Maybe you can persuade him to give me the key," Michaud testified. However, before that request was acted upon, another member of the group found the room key, Michaud said. Pulliam and the others then removed about 5 antennas from the store, Michaud testified.

Stanley J. Reed, Pulliam's attorney, said cancelled checks and other bank records the government plans to present at the trial are "totally consistent" with Pulliam's account. "Your interpetation of the paper trail depends on whom you believe, Mr. Butler or Mr. Pulliam," Reed told the jurors. He said that Butler, who had financial problems and who feared losing his private investigator's license because of his role in the loan, "has plenty of motive to testify falsely in this case."

Prosecutor James P. Ulwick told the jurors "some of you may not like Gordon Butler" who was named in the Pulliam indictment as an unindicted coconspirator, but "his testimony will be corroborated in every way." When Jefferson officials confronted Pulliam last September about the loan, Ulwick said, Pulliam "immediately contacted Butler and tried to cover up the whole thing."