The door to Room 180 was still sealed. An Afro comb and a bottle of nasal spray were still on the dresser, just where Vernon Jordan left them.

Outside, about 70 feet away, a tall, powerfully built black man in a dark blue business suit was pacing up and down alongside the chain-link fence bordering the parking lot of the Marriott Inn. He stopped and stared at the cars passing by in the night. Then he began pacing again, brooding over the mystery of what had happened just a few yards away.

The mystery has, if anything, deepened since the man in charge of the federal investigation into Jordan's shooting, FBI agent Wayne Davis, paid his lonely visit the other night to the scene of the crime. Ostensibly promising leads have been checked into oblivion. Initial suspicions have been discarded. A belated search of a four-mile stretch of Interstate 69, which runs past the hotel, has proven fruitless. Jordan's room has been unsealed by police, cleared and rented out again.

The investigation is "dead," Allen County prosecutor Arnold Duemling asserted today, choosing the word with care. In police parlance, he said. "That means you are without a viable lead -- without a concrete, viable lead."

Even hypnosis has been tried on a potential witness, to no avail.

At a news conference in the City-County Building here this afternoon, the deputy Fort Wayne police chief, Ernest Walters, said hypnosis was administered yesterday by state police to a woman who thought it might help her recall more details about a parked car she reported seeing in the area close to where Jordan was shot at 2:05 a.m. last Thursday. The results were negative.

Reflecting the dimming prospects for an early solution, Mayor Winfield Moses Jr. announced that the press briefings held every day since the May 29 shooting are being dropped "until we have further information to report."

Twelve city detectives are working full-time on the case, still a major commitment for a city the size of Fort Wayne (pop. 188,800), but far less than the full complement of 30 initially thrown into the investigation.

"We have to keep the regular concerns of the city in mind too," the mayor explained.

Across the street, in the Allen County Courthouse, prosecutor Duemling said the idea of the crime's having been committed by some jealous acquaintance of Jordan's companion that night, Martha C. Coleman, was too remote to deserve further consideration.

"There is no evidence at this point that any of her former husbands or associates had anything to do with the crime," Duemling told reporters. Under questioning by city police yesterday, he related, she said, "she knew of no one in her life, past or present, who would do something of that nature."

He said Coleman "just happened to be in the wrong place at the wrong time," when Jordan was shot.

A member of the board of the Fort Wayne Urban League, Coleman was introduced to Jordan, the League's 44-year-old national president, following the local chapter's annual dinner here, then met him for drinks around midnight in the hotel bar.

Around 12:40 a.m. the two left the hotel in Coleman's Grand Prix for a twenty minute drive to her house to have coffee, she told investigators. He was shot on their return to the hotel as he stepped out of the car, about 50 feet from his room.

Offering the first public explanation of the long ride for a cup of coffee, Duemling said Coleman told police she was very proud of her home and of an antique collection she had put together over the years, and so she invited Jordan over. She proposed breakfast, but Jordan agreed to come just for coffee, the prosecutor said she said.

The interview was videotaped at Duemling's suggestion and Coleman also agreed to take a polygraph test that the prosecutor proposed to verify her story.

Duemling said he did this "purely as a matter of professional thoroughness." He said he does not expect the test to show any discrepancies in her account. Details of the examination have yet to be worked out with Coleman's lawyer.

The prosecutor said he thinks that Jordan was ambushed from a grassy slope overlooking the hotel's brightly lit parking lot by "someone from outside the community," but the only reason he offered for this theory was hometown pride in this thoroughly middle-American town. (National advertisers continually use Fort Wayne as a testing ground for products ranging from Hamburger Helper to Playtex girdles to Baker Tom's cat food.)

"I was born and raised here," Duemling said. "This type of behavior is totally inconsistent with the people of this community."

Fort Wayne does have a Ku Klux Klan chapter, which staged a parade that drew 34 people last September. Most residents and officials insist that it is inconsequential. "We have our militants," Dueming said, "but not in the sense of violence, nothing of the sort."

Declaring that he was encouraged by the FBI's involvement, especially because of its nationwide "network of informants," the prosecutor said solution of the case hinges on whether a tipster emerges.

At his news conference with city police, Mayor Moses confirmed that the FBI located two other witnesses who had just arrived at the hotel and heard Jordan call for help after being shot. But, the mayor emphasized, "They are not witnesses in the sense of having seen the crime."

Chief Walters refused to say whether he agreed with Duemling's characterization of the investigation as "dead." Both the police and the FBI, which has 20 agents working on the case here, prefer to describe it as "continuing." FBI officials do not contest the point that there are no "concrete, viable leads," but they say there are still plenty of angles that must be checked out and much work to be done.

Said FBI spokesman Roger Young in Washington: "I've been in investigations that are flat dead and this is not one of them by any stretch of the imagination." But he acknowledged that "just to check out what we've got going now is going to take weeks."