Eighty-six percent of the parking tickets issued to diplomats in Washington go unpaid, according to the District of Columbia officials. Between July 1981 and October 1982 that amounted to 18,358 unpaid tickets worth $451,180 in fines and penalties.

But members of diplomatic missions get away with less illegal parking than they used to. Since 1979, when the district made parking violations a civil, rather than criminal matter, lower-level diplomats who fail to pay parking tickets can have their cars impounded or "booted."

But those who retain full immunity still can't be forced to pay. The latest computer printout of the delinquent diplomats lists 5,542 unpaid tickets issued between July 1 and Oct. 31, 1982. The country most often cited on the list is the Soviet Union (1,349 tickets), then Saudi Arabia (231 tickets) and Nigeria (185 tickets).

Soviet spokesman Vlydimir Mikoyan said his embassy has no obligation to pay for tickets because of an agreement with the State Department that allows U.S. diplomats to ignore parking restrictions near the U.S. Embassy in Moscow and Soviet diplomats to park in the congested area near their embassy.

The person on the list named most frequently, Ahmed Said, an Egyptian press attach,e, accumulated 60 unpaid tickets ($1,360 in fines and penalties) from July through October. He says that "parking is very, very difficult."

In the same four months, Hisham and Nouha Alhegelan, the son and wife of the ambassador from Saudi Arabia, accumulated 68 unpaid tickets ($1,640 in fines and penalties). The son, a student at American University, says all the tickets were his responsibility, that he didn't mean to abuse his diplomatic immunity but "it was forgetfulness. If I broke the law I'm only too happy to pay the fine . . . I don't remember getting any second notices. My father wouldn't condone it if I didn't pay.