The Metropolitan transit Authority put its new $10 million rapid-transit cars into service on the Cambridge Dorchester subway this morning with a personal incentive for early risers.

Pretty girls pinned corsages on the first 300 women to board a new, four-car train as it pulled out of Harvard Square at 6:20 a.m. Men were handed free cigars as mementos of the inauguration of the new train.

Women were allowed to wear their corsages on the train, but men had to wait until leaving the coaches before lighting up.

Bearing the colors of Massachusetts, the first blue, white, and gold train will continue in service until 6:07 p.m. today, the Boston Globe reported yesterday. A second, which left Harvard Station at 6:48 a.m., will remain in operation until 5:33 p.m. A third rolled out at 7:08 a.m. and will continue rumbling along the tracks until 5:55 p.m.

General Manager Thomas J. McLernon said last week at a preview for public officials and business leaders that an entire 92-car flee of new trains will be in operation by July. The new trains replace 114 old coaches, some of them over 50 years old, which will be sold as junk.

Besides the new rapid transit cars, the MTA has also purchased 400 new buses. Many will be used when the $1.5 million demonstration experiment with the Mass Transportation Commission goes into effect this June.