The federal government has refused to contribute to any financial settlements for families of three of the seven astronauts killed in the Challenger shuttle crash, asserting that it has no legal liability in the accident.

The most recent of these settlements came last week when the father and brother of mission specialist Judith A. Resnik signed an agreement with shuttle contractor Morton Thiokol Inc. for payments said to total $1.5 million to $2.5 million.

Although the government contributed to similar settlements with four of the Challenger families in December 1986, it has since turned down claims arising from the nation's worst space accident, according to lawyers involved in the cases. Michael Oldak, a lawyer representing the Resniks, said the Justice Department cut off negotiations with him several months ago and refused to offer anything.

"The government for some reason was trying to screw us," said Marvin Resnik, the astronaut's father. "We feel the attorney general's office did not bargain in good faith . . . . She lost her life just as much as any of the others."

Justice Department spokeswoman Amy Brown confirmed yesterday that the government has declined to participate in any further settlements with Challenger families, other than the four that it negotiated on behalf of the National Aeronautics and Space Administration and Morton Thiokol in 1986. Besides Resnik, the government did not make payments to Ronald E. McNair's family, which also settled separately with Thiokol. A suit filed by the widow of Challenger pilot Michael J. Smith against NASA and Thiokol is pending.

Department officials have argued that it would be unfair for them to contribute to any settlement higher than the amounts negotiated in 1986.

Citing the survivors' privacy, the department has never released the settlement terms. But U.S. District Court Judge Charles R. Richey, during oral arguments on a freedom of information lawsuit filed by three news organizations, told department lawyers yesterday that an "overriding public interest" justified release of at least the total amount paid to all four families and what portion of that total was paid by Morton Thiokol.

In the case of the Resniks, spokeswoman Brown said, the family had initially rejected a "very generous" settlement offer that was based on the formula used to compute the secret payments received by the four other Challenger families.

The Justice Department's initial offer -- on behalf of NASA and Morton Thiokol -- was estimated by Oldak to be worth "several hundred thousand dollars," a figure he said was substantially less than that offered the other families, apparently because Resnik was the only Challenger crew member who was not survived by a spouse and children.

According to court papers filed in the freedom of information suit, Justice officials, seeking to avert "highly complex tort litigation," began meeting with some of the Challenger families soon after the accident in an effort to reach an overall settlement. The families were urged not to retain private counsel and to accept the compensation offered by Justice in order to avoid any further damaging publicity, according to two lawyers who were retained by the astronauts' families.

Ronald Krist, who was retained by McNair's widow, said his attempts to negotiate with Justice were "fruitless." They told him "if I was not going to fall in line with the other widows, then they were not going to contribute," he said.