Democratic Party officials said yesterday that a fund-raising dinner at the Washington Hilton last week may have been the most financially successful such affair in recent history.

Susan Morrison, the chief press officer of the Democratic National Committee, said party officials estimate the $1,000-a-plate dinner will end up netting the debt-ridden party about $1 million. She said a final tally will not be available for a few weeks.

President Carter was the main speaker at the dinner, which attracted about 1,200 party officials and contributors from around the country.

Before the dinner, the party was saddled with about $1.6 million in debts, chiefy from the 1968 presidential campaign of the late senator Hubert H. Humphrey (D.-Minn.) and the 1972 campaign of Sen. George McGovern (D.-S.D.). The party also is running about a $700,000 deficit in its current operating budget, Morrison said.

Only a portion of the expected $1 million profit from the dinner will be used to retire part of the debt. The remainder, Morrison said, will be used for contributions to Democratic congressional candidates, to finance the party's midterm convention, scheduled for December in Memphis, and to "pay our bills and keep the committee running."

The DNC expects to contribute about $100,000 to Democratic candidates in this fall's congressional campaigns. Morrison said the cost of the midterm convention is currently estimated at $400,000.

The DNC has sponsored four other similar fund-raising dinners since Carter took office. The others, in Los Angeles, Atlanta, New York and Houston, netted between $400,000 and $800,000 each, with the Atlanta dinner being the most successful until last week's affair.

Morrison said the Washington dinner was so successful probably because "it was the first one in 12 year to be held in Washington with a Democratic president and a Democratic Congress."

She said the DNC plans no other major fund-raising activities this year.