Jessica Savitch, the NBC television reporter who became one of the first women to anchor an evening network newscast, was killed late Sunday night after the car she and a companion were in drove into a canal in a rural section of Bucks County, Pa., and overturned.

According to officials in Bucks County, Miss Savitch, who was 35 years old, and Martin Fischbein, 34, the vice president and assistant general manager of The New York Post, were found inside a station wagon that was upside down in five feet of water in the Delaware Canal near New Hope, 30 miles northeast of Philadelphia.

In her six years at NBC, Miss Savitch served as the anchor of weekend editions of ''The NBC Nightly News'' and ''NBC News Digests,'' the one-minute prime-time news updates, and made frequent appearances on ''Meet the Press'' and the ''Today'' show. She also worked as a correspondent in Washington, reported on the 1980 Presidential campaign and was the anchor of a PBS documentary series, ''Frontline.''

Miss Savitch received four Emmy Awards and the Alfred I. Dupont-Columbia University Award for local reporting. She resided in New York City. Drove Wrong Way

Walter Everett, the New Hope police chief, said that the couple had driven the wrong way out of the parking lot of a restaurant, Chez Odette, where they had gone for dinner. They drove about 600 feet over a dirt-and-gravel area, and past two warning signs. The car fell 10 feet from the canal wall into the water and landed upside down.

''It was raining, the weather was bad,'' Mr. Everett said. ''The visibility was very poor.'' He said there had been a similar death there some years ago.

''The mud was knee-deep on the bottom,'' said Mario Lasarro, a member of the Lambertville, N. J., rescue squad that went to the scene on rural River Road. ''It looked like they tried to kick the doors open but they couldn't.'' Miss Savitch was in the back seat, Mr. Everett said, and Mr. Fischbein was in a seat belt at the wheel.

An autopsy showed that both Miss Savitch and Mr. Fishbein died of suffocation due to drowning, according to Dr. Thomas J. Rosko, the Bucks County coroner. He said that Miss Savitch had suffered a slight head injury, but it did not contribute to her death. Both she and Mr. Fishbein died ''within one minute to a very few minutes'' after plunging into the canal, he said.

There was no evidence to suggest alcohol or drug abuse, Dr. Rosko said, but he said that toxicological tests would not be completed for a week.

Tom Brokaw, the anchor of ''The NBC Nightly News,'' said: ''She was a dedicated, hard-working broadcaster who felt very strongly that women should have a more active role in the profession.'' Radio Work as a Student

Miss Savitch was born in 1947 in Kennett Square, Pa., daughter of Florence and David Savitch. While in high school in Atlantic City she got her first job in broadcasting, as a disk jockey and a news reader at radio station WOND in Pleasantville, N. J. ''I loved everything about the radio station,'' Miss Savitch said in her autobiography, ''Anchorwoman,'' published in 1982. ''At last I felt that I belonged.''

While Miss Savitch attended Ithaca College in upstate New York, she worked as a disk jockey at radio station WBBF-AM in Rochester. In 1969, after receiving her bachelor's degree, she was hired as a researcher for CBS radio. The following year she became a general assignment reporter at KHOU- TV, the CBS affiliate in Houston.

In 1972, she became a reporter and anchor for KYW-TV in Philadelphia. Miss Savitch worked on several award- winning documentaries and special reports there, including a five-part series, ''Rape . . . the Ultimate Violation,'' in which she spent two weeks working as a decoy with a police undercover unit. The series won her a Clarion Award from Women in Communications Inc.

Miss Savitch was hired by NBC in September 1977 as a Congressional correspondent. She also contributed to ''Prime Time Saturday'' and ''Prime Time Sunday,'' NBC news magazines. Since last summer, when Connie Chung took her place as the anchor on the Saturday ''Nightly News,'' she had delivered the network's weekday news updates.

Miss Savitch had suffered a number of personal misfortunes in recent years. Her first marriage, to Mel Korn, a Philadelphia advertising executive, ended in divorce after less than one year. She was married in 1981 to Dr. Donald R. Payne, an obstetrician- gynecologist, but five months later she discovered her husband dead in their home, an apparent suicide.

She is survived by her mother and two sisters, Lori and Stephanie Savitch of Margate, N.J