Five persons, including a pregnant 31-year-old Lexington Park, Md., woman and her three children, were killed yesterday in a fiery two-car collision on Rte. 5 in Charles County that came after the car she was riding in spun out of control on a curve known as Dead Man's Turn, authorities reported.

The woman's husband, who was driving the family's car, a 1972 Mustang, was one of two persons critically injured in the accident, which occurred shortly before 3 p.m. about one mile north of the St. Mary's County line, according to the Charles County Sheriff's Department.

Officer J.J. Fenlon of the sheriff's department said the Mustang skidded out of the curve and into the path of an approaching 1987 Nissan Sentra. The Mustang was struck near its gasoline tank and burst into flame, he said.

Fenlon listed the primary cause of the crash as "speed too great for conditions."

The dead woman was identified as Patricia Day Smith. The three children were listed as Melanie April Smith, 6, Cassandra Blair Smith, 3, and Jacqueline Amber Smith, 7. The husband was identified by the sheriff's department as John Walter Smith III, 31.

He was listed in critical condition last night in the intensive care burn unit at the Washington Hospital Center.

The fifth person killed was listed as Daniel Thomas Fitzgerald, 32, of Lexington Park. Fenlon said he was a member of the armed forces but he could not give details.

The Sentra in which he was riding was driven by his brother, Anthony Fitzgerald, 25, of Floral Park, N.Y., who was visiting, Fenlon said. Anthony Fitzgerald, who suffered internal injuries, was listed in critical condition last night at Prince George's Hospital Center.

Full details of the accident were not available late last night, but Fenlon said the Smiths' Mustang was headed north on Rte. 5 just before the crash.

Witnesses said that about the time of the crash it rained briefly in the area, which is about a mile south of Hughesville and about 30 miles southeast of Washington. Fenlon said a wet road may have played a part in the collision.

He said the Mustang went out of control on Dead Man's Turn, which he described as a "sharp curve" in the four-lane blacktop highway, which has a posted speed limit in that area of 50 miles an hour. It has been the scene of numerous accidents.

As the Mustang emerged from the curve, he said, the vehicle "hydroplaned" on the wet surface and spun "almost 180 degrees," entering the southbound lanes.

He said the Nissan, which was southbound and had not yet entered the curve, hit the Mustang "in the gas tank area on the driver's side" and "it immediately burst into flames."

The impact of the crash jammed the front end of the Sentra into the The Mustang was struck near its gasoline tank and burst into flame.

passenger compartment, Fenlon said.

A Maryland state police helicopter landed on Rte. 5 and took Smith to the Washington Hospital Center. A U.S. Park Police helicopter took Fitzgerald to Prince George's Hospital Center, according to Capt. Tony Rose of the Hughesville Volunteer Fire Department.

Rose said Daniel Fitzgerald was taken by ambulance to Physicians Memorial Hospital in La Plata, where authorities said he died shortly after arrival. Staff writers Christopher J. Georges and Keith Harriston contributed to this report.