FBI agents today pursued their investigation of a possible conspiracy in the shooting of civil rights leader Vernon Jordan, partly because of the discovery of three tamped-down areas on the grassy slope from which he was ambushed.

Fort Wayne police, however, were skeptical that more than one gunman was involved in the incident early Thursday.

"There's nothing to indicate that there's more than one," said Police Chief Leon Wolfe. "You can lay down in the grass for a minute and leave an impression."

Jordan, the 44-year-old president of the National Urban League, was reported in "guardedly good" but still serious condition today.

His chief surgeon, Dr. Jeff H. Towles, told reporters at Parkview Memorial Hospital that the shot from a 30.06 rifle left a hole in Jordan's back "almost large enough to put a fist in." He said Jordan was lucky to be alive because the bullet barely missed his spinal column.

Federal and local authorities still have no identifiable suspects, but they are looking for the occupants of a dark-colored Chevrolet, three young white males, who may have yelled some racial epithets at Jordan and his companion as they were driving back to the Mariott Inn shortly before the shooting.

Jordan's companion, Martha C. Coleman, 36, told police that her car windows were rolled up at the time of the incident. According to Fort Wayne Police Capt. Gary Lotter, "It was not clear what was said," but authorities said Coleman said that some racial remarks had been made by the occupants of the other car, which then sped from sight.

The incident took place about 1:45 a.m., about 20 minutes before Jordan was shot as he got out of Coleman's red Grand Prix in the hotel parking lot near his room.

Two, perhaps three, shots were fired, police say. Shots came from a grassy triangular area that overlooks the parking lot but is separated from it by an exit ramp of Interstate 69.

FBI agents said today that there were "three areas of tamped-down grass" on the slope, not one, as originally reported. They pointed out that "this coincides with the number of "individuals" in the car that passed Coleman's Grand Prix.

"It could be purely a coincidence. It could be the same guy moving around," one agent said. "But the marks were not made by somebody just walking through that area."

He called it one of a number of leads that must be pursued before the possibility of a conspiracy can be ruled out.

In Washington, FBI spokesman Roger Young said that Police Chief Wolfe "may be entirely right" in suspecting a lone gunman, but Young emphasized, "We're not backing out until we're satisfied."

Some black leaders voiced dissatisfaction with the conflicts in initial police accounts of the attempt on Jordan's life -- such as talk at the outset that the weapon had been of small caliber -- and with the failure of officials to disclose the questioning of several individuals about the shooting until after they had been released.

"On the one hand, the preoccupation [of local authorities] is with keeping calm," the Rev. Jesse Jackson said on entering the hospital today to visit Jordan. "Our preoccupation is seeking justice. And we think that people will respond more rationally if they know the truth than if they suspect there's a coverup being attempted."

In a similar vein, Jackson, leader of Operation PUSH, joined four other black leaders in a telegram of President Carter urging him to leave "no stone unturned" in the federal investigation. The other signers were Dr. Joseph Lowry, president of the Southern Christian Leadership Conference; Benjamin Hooks, executive director of the NAACP; C arl Holman, president of the National Urban Coalition-and Mayor Richard Hatcher of Gary, Ind.

"It is of the most critical importance that the perpetrator or perpetrators be brought swiftly to justice so that it is clear that our national government will not tolerate this brutal assault upon a man who has given so richly of himself to minority and poor Americans," they said.

After the shooting early Thursday, two women employes of General Telephone's Data Services Center, located across Interstate 69 from the Marriott, reported having seen a car parked along the exit ramp shortly before the attack.

They reportedly saw the car during a 2 a.m. break and told their supervisor about it. When the supervisor went outside a short time later, the car was gone.

Allen County sheriff's deputies, it was disclosed today, arrested a motorcyclist toting three rifles, including a .30-06, around 9:30 Thursday morning, but did not tell Fort Wayne police about it until 5:45 p.m., shortly after the man had been released on his own recognizance.

The cyclist, John T. Douglas, 40, of Grabill, Ind., had been picked up on charges of drunken driving and driving with a suspended license. Authorities said he told them he had been home asleep at the time of the shooting and had gotten up around 5 a.m. ostensibly to report at his machinist's job at 7 a.m.

Sheriff Charles Meeks said Douglas said he went drinking instead, around 6 a.m., and ran into a friend at a suburban shopping center who offered to sell him the three rifles.

Douglas reportedly told officers he went to the man's house to get the guns -- an Enfield 303, a .22-cal. rifle and the 30.06 -- and paid $100 for them, but the sheriff said Douglas was "too intoxicated" to remember much. The "friend" has yet to be located.

The weapons were confiscated, however, and the .30-06 has been sent to FBI headquarters in Washington for ballistics tests. Meeks said none of the guns seemed to have been fired recently, but he said he would be "a lot more comfortable when we get the ballistics [reports] back and when we can identify the individual he [Douglas] got the weapons from."

Asked why city police investigating the Jordan shooting weren't notified before Thursday evening, the sheriff said his office hadn't realized they were looking for a .30-06 cal. rifle. That fact, however, had been announced at a mid-afternoon news conference.

Police also questioned and released a Chicago man who had been staying at the Marriott hotel and who allegedly made some racial remarks to Jordan and Coleman in the hotel bar before the shooting. Capt. Lotter said his detectives were satisfied that the man had nothing to do with the attack.

Jordan was here to address the Fort Wayne Urban League's annual dinner. Around midnight Wednesday he left the dinner with Coleman, a member of the Urban League's board here, to have coffee with her and other friends at her home. She drove Jordan back to his hotel around 2:05 a.m. He was shot as he walked around the back of the car.

Police have not completed their questioning of Coleman, who quickly summoned a lawyer. She was not entirely cooperative in the first interrogation, Lotter said.

Asked about the results of any further questioning, Lotter said, "We're still conversing with her attorney," Charles Leonard, who declined to talk to reporters.

Neither the police nor the FBI has been able to question Jordan at any length. Towles said Jordan was "alert . . . curious . . . and inquisitive" this morning, asking questions and wanting to read the paper. But FBI agents were able to talk to him around noon for only about 10 minutes.

"He looked terrible," one agent reported.

Shirley Jordan visited her husband tonight and said he was in good spirits. As for the shooting, she said, "We didn't discuss it."

Towles said Jordan would not be able to leave the hospital for some time. His physicians say they believe there is no paralysis, and a numbness from a leg wound seems to be disappearing. Jordan suffered the leg wound from what police believe was the fragment of a second bullet that may have shattered when it hit the chain-link fence separating the hotel's parking lot from the interstate ramp.

The federal inquiry is being directed here by Wayne Davis, the black special agent in charge of the FBI's Indianapolis office. He called the shooting "a deliberate act" and said "it doesn't appear to have been happenstance, a joyride or anything else." But he stopped short of calling it an "assassination attempt."

A conspiracy "can be a personal thing," Davis told reporters. By definition," all it takes is two or more people. As for motives, Davis said, "we haven't ruled out anything yet."