Critics of the proposed Rosecroft Raceway Metro line in southern Prince George's county have submitted a report to Maryland's transportation secretary which argues that tate finding for the line should be held up because of irregularities in the selection of the Rosecroft alignment over one along Branch Avenue farther north.

Although the Prince George's County Council has favored the controversial extension of Metro's green line from Anacostia to Rosecroft Raceway in separate three votes over the past 18 months. Transportation Secretary James O'Donnell must approve the move before the state can pay its share of the line's construction costs.

O'Donnell has delayed state approval of the Rosecroft alignment because of continuing debate over the substitution of that plan by the council for the Branch Avenue Line, which was included in Metro's plans from 1968 until last year.

Proponents of the Branch Avenue Line, including three Prince George's state delegates and a potential developer along the Branch Avenue corridor, argued in a report submitted to O'Donnell Friday that studies of the two green line alignments had distorted ridership, construction and operating cost figures in favor of Rosecroft.

Those charges come in addition to repeated allegations over the past year that the county council's selection of Rosecroft Raceway as a Metro stopping point was improperly influenced by Peter O'Malley, a former Democratic Party Leader who is the attorney for the raceway and for property owners nearby. O'Malley and county council members have denied those charges.

O'Donnell requested the report from the Branch Avenue supporters after a meeting earlier this month. He is expected to decide on whether to commit the state to the Rosecroft Raceway line within the next two weeks, according to Del. Lorraine Sheehan (D-Prince George's), a member of the Branch Avenue group.

"What we're hoping is that O'Donnell will send this back to the country and ask them to answer the questions we have raised." Sheehan said yesterday. a

The group's report was prepared by Jon F. Oster, an attorney who was hired by Joseph Smith and Sons, Inc., which is planning major developments on the Branch Avenue line if the alignment is ever switched back.

The report argues that the ridership figures prepared in 1977, when both lines were still under consideration, favor the Rosecroft alignment by including 3,000 riders on the Rosecroft line that would be added by a proposed feeder bus system along Suitland Parkway -- a bus system that would replace the Branch Avenue line.

This bus system, the report charges, is logistically impractical and would never be approved or funded by Prince George's County or the District.

In addition, the report argues that ridership figures for the Branch Avenue line were underestimated, that construction costs were overstated by $20 million for Branch Avenue and understated by $53 million for the Rosecroft line.

If true, the report's conclusions would eliminate two of the major arguments of supports of the Rosecroft line -- that peak ridership would be higher there than along Branch Avenue and that construction costs would be far lower.

Sheehan said yesterday that she believed that the ridership and construction cost figures had been delibertely distorted by county planners who conducted the studies, but not for the political reasons that have been attributed to the county council's decision.

"They are planners," Sheehan said. "And planners like to look into the future and draw lines, and see all kinds of development at Rosecroft that is now not going to happen. Then they get themselves locked into their figures and have to defend them."

County planners yesterday defended the figures used in the selection of the Rosecroft lines at the best available at the time, however, and several officials questioned the assumptions made in Oster's report.

"If we ran those surveys again we wouldn't get the same numbers, because you get different figures every time you do them," said Frank Derro, the chief of county transportation planning. "But at the time we did we had, and with those the lines were accurately compared. There was no hanky-panky."

County council member Francis B. Francois, the county's representative on the Metro board and a long-time proponent of the Branch Avenue line, added: "The studies at the time made sense. Since that time the facts have changed, and no one can guarantee the ridership at Rosecroft. But no one can guarantee the ridership for Branch Avenue, either."

Francois said he believed that O'Donnell should now approve the Rosecroft line because of the council's repeated votes for it. "It has been the state's position for several years that it was up to the county to decide this question," he said. "I frankly expect O'Donnell to go along with what the county has decided."