A 23-year-old man yesterday was charged with the murder of Ronald J. Pettine, the former Morris K. Udall campaign aide whose battered nude body was found near the Iwo Jima Memorial last Oct. 2.

U.S. Park Police identified the suspect as Thomas S. McDonald, who is unemployed and has no known address. He was held in the Alexandria jail last night in lieu of $100,000 bond, following arraignment before U.S. Magistrate Harris Grimsley.

McDonald reportedly approached a Richmond police officer Thursday night in a bus terminal in the state capital and said, "I'm the guy everybody is looking for in the killing of Ronald Pettine," according to a U.S. Park Police spokesman. Richmond police held McDonald overnight on a fugitive warrant.

McDonald was taken to the Northern Virginia federal magistrate's court yesterday afternoon. At the same time, his car was being impounded near the C&O Canal in Montgomery County, Park Police spokesman George Berlacy said.

The car, with keys in the ignition but with its door locks broken, was found near Lock 6 of the canal, just off MacArthur Boulevard in the county's Brookmont section, according to Park Police. Police woul dnot say how they learned the car was by the canal or why it might have been left there.

It was not clear last night who McDonald is, as police said several addresses given by him turned out to be incorrect. The address Alexandria jail officials have for McDonald is in an expensive residential neighborhood of Montgomery County, where the residents said they had never heard of anyone named Thomas S. McDonald.

The Iwo Jima Memorial, where Pettine's body was found, has been a well-known homosexual meeting place for several years, and the site of many arrests for sodomy and numerous sexual-related beatings. The underbrush in the six-acre wooded area surrounding the monument in Arlington has since been cut down. There have been no arrests or assaults there since October, Berklacy said.

The scenic memorial, located beside Arlington National Cemetery, has long been one of Washington's more popular tourist attractions by day, but for at least six years has been a popular homosexual haven by night. It was also a place for those who preyed on homosexuals, according to Park Police.

Three men beat up a fourth there just three weeks prior to Pettine's murder and a man was stabbed there early last summer. In still another case, four soldiers were arrested and charged with assault last July after allegedly forcing a man into their car at the memorial, stripping and beating him and then dumping him along the George Washington Memorial Parkway.

Police undercover agents arrested as many as 103 men there on sodomy charges within one two-month period in 1975 and 60 had been arrested within the two months prior to Pettine's death. The memorial grounds have been deserted at nights since the muder, Park Service spokesman Berklacy said.

Pettine, 32, a bright political technician who directed scheduling and advance work for Udall's presidential bid last spring, had been a deputy secretary of state in Pennsylvania and helped engineer the revision of that state's election laws. He had also been a campaign aide to Sen. Hubert H. Humphrey (D-Minn.) during his 1968 presidential campaign and was appointments secretary for Pennsylvannia Gov. Milton Shapp's gubernational campaign in 1970.

Married and the father of two children, Pettine was also a sometime homosexual, according to at least four people in the Udall campaign. He was unemployed at the time of his death, but had been looking forward to a job on Capitol Hill after last fall's elections.