The Department of Transportation has held "preliminary talks" with officials of the bankrupt Milwaukee and Rock Island railroads aimed at a possible merger or consolidation.

The Milwaukee, which is officially known as the Chicago, Milwaukee, St. Paul and Pacific Railroad announced plans to file for reorganization under Chapter 77 of the Bankruptcy Act yesterday. The railroad, 12th largest in the country, reaches 16 states on 10,000 miles of track.

The Rock Island, officially the Chicago, Rock Island and Pacific, went bankrupt in 1975.

Officials of the two lines met with Robert E. Gallamore, Deputy Administrator of DOT's Federal Railroad Administration, yesterday. The discussion reportedly centered on alternatives that could expedite the procedure for merger under special rules of the Railroad Reorganization Act.

"These were very preliminary discussion, with only a tentative inquiry being made," a DOT spokesman said.

But Rock Island president John W. Ingram said in a telephone interview from Chicago, "We are looking for places where we can get together . . . where there is some duplication."

He pointed to the consolidation six months ago of the two railroads' operations from Iowa's Quad Cities to Kansas City. "We both use our lines there," Ingram said, "to our mutual advantage."

Ingrahm, a former administrator of the FRA, said the Rock Island is "looking to do the same things in other places."