WASHINGTON (AP) _ A $622,905 Justice Department grant to a conservative women's group planning to educate the public about family violence may be illegal, Rep. Patricia Schroeder, D-Colo., said Wednesday.

The grant was made last month to the Task Force on Families in Crisis, an offshoot of the Eagle Forum group headed by Phyllis Schlafly.

It comes nearly a year after the Justice Department, over the objections of Mrs. Schlafly and other conservatives, awarded $580,000 to the National Coalition Against Domestic Violence. The coalition members run most of the nation's shelters for battered women.

Mrs. Schroeder, a member of the House Judiciary Committee, said she will ask the committee to investigate the grant to the conservative group. Her press secretary said a General Accounting Office probe may also be requested.

''Phyllis Shlafly doesn't even believe that domestic violence occurs and that they should have shelters for this. This grant, as far as I can ascertain, is totally illegal,'' Mrs. Schroeder said in a speech on the House floor.

She contended the Justice Department had already spent most of its domestic violence money and did not have enough left for a grant the size of the one awarded to the Schlafly group.

''Secondly, the money could only be spent for shelters, not studies. This money is totally for studies. Thirdly, it was to go to groups that had experience in the area. This group has no experience whatsoever in the area of domestic violence,'' she said.

''And finally the group itself had withdrawn its grant proposal last April, saying it shouldn't take money from the Justice Department at a time the government is making so many debts,'' Mrs. Schroeder said.

The Task Force on Families in Crisis plans to educate the public to the problem of domestic violence and enlist religious and civic groups in five demonstration cities to help prevent it, according to Assistant Attorney General Lois Herrington, director of the Office of Justice Programs.

She said the task force would bring the problem of family violence home to mainstream America.

''We've finally got a group that is very representative of a lot of these civic groups, that has ties to civic groups, ties to the religious community that we have not had before,'' said Mrs. Herrington. ''This is real important. It's as important as our shelter grant because there's a lot of things you can do along the way to prevent family violence.''

Mrs. Herrington said the money for the Task Force on Families in Crisis came from the same discretionary fund as the grant to the National Coalition Against Domestic Violence.

She said five of the people on the task force had testified on family violence during Justice Department hearings around the country, and that they had either personal or professional experience in the area.

She said the Schlafly group reinstated its grant application when it became apparent that the department had the money to fund it. The application included an acknowledgement that shelters are necessary in some instances, she said.

People For the American Way, a liberal lobbying group, called the grant ''a scandalous abuse of public funds'' that would help the Eagle Forum spread its views with taxpayer dollars.

In her written text, Mrs. Schroeder said the Schlafly group appears to have gotten the grant merely to ''get even'' for last summer's award to the National Coalition Against Domestic Violence.

''To give away $622,905 of the taxpayers' money merely to assure Phyllis Schlafly that the Justice Department has not sold out to the feminists is an absurd abuse of the taxpayers' money,'' she said.

Mrs. Herrington said Phyllis Schlafly was not involved in the obtaining the grant. She said the money would be used to carry out prevention activities that were recommended in September 1984 by an attorney general's task force on family violence, and the project is supported by the coalition that received money for shelters last summer.

In commenting on the grant Tuesday, Mrs. Schlafly had told The Washington Post that ''fair play required equal treatment of traditional women.'' She said she disagrees with the notion that ''all men would be wife-beaters if they got the chance ... Surely the whole answer cannot be to punish the woman by taking her out of her own home.''