About 2,500 Hungarian-Americans marched to the White House and then to the Capitol yesterday to protest the Carter's Administration's plan to return the Holy Crown of St. Stephen to Communist-ruled Hungary.

Carrying red, white and green Hungarian flags, a huge black cross and a replica of the golden crown, the demonstrators sang Hungarian songs and heard a dozen senators and members of Congress speak against the return of the crown to Hungary.

At the Capitaol Rep. Mary Rose Oakar (D-Ohio) told the marchers she has been assured by Carter Administration aides and representatives of the National Security Council that the discussions about the return of the crown to Hungary have been postponed until January.

Oakar, whose westside Cleveland district includes many Hungarians, said she was told that "Secretary of State Vance will not return the crown in December," as was planned because of protests. She called the decision by the Carter Administration a "big change."

"The return of the crown will mean that the United States is giving its approval to the Communists in Hungary," said Lel Somogyi, 23, a computer systems analyst from Madina, Ohio. Somogyi's parents were refugees from Hungary after World War II.

"A spit in the face, an insult to people who have fought for freedom in Hungary, that is what Carter and his human rights are doing," said an elderly Hungarian from New Brunswick, N.J. who claimed to have fled his native country during the 1956 attempt to overthrow the Communists.

"The crown is more than a symbol or a museum piece," said Andrea Vareska, a Cleveland attorney whose parents escaped Hungary after World War II. "It is the possession of the true rulers of Hungary and the United States should not make the communists the true rulers. There is hope as long as the communists never get their hands on the crown."

The Holy Crown of St. Stephen was smuggled from Hungary to Austria at the close of World War II and given to American troops by 28 Hungarians who had pledged their lives to protecting it. Later brought to America, it reportedly is kept in Fort Knox, Ky.

The crown was a gift to Stephen, first king of Hungary, from Pope Sylvester II in 1001.

Last Nov. 4, on the 21st anniversary of the 1956 attempt to overthrow the communist regime, President Carter said returning the crown would help imporve relations between Hungary and the United States.