Iraqis turned out in large numbers today to vote in elections for their first national assembly in more than 20 years.

At one key center, the northern city of Mosul, almost half of the voters at three election centers cast their ballots within the first three hours after the polls opened.

The vote count was to begin at 8 p.m. and the first results probably will be announced early tomorrow. Officials said they expected an 80 percent turnout which probably would be reflected in Baghdad and in main provincial towns and cities.

More than 6 million Iraqis 18 years and older were eligible to vote, including women for the first time in the country's history.

"I don't know if it will be good, but I sure do hope so, and I'm glad to be able to do it," said 65-year-old Shahim Isho Ibrahim Bazzi, a watchman casting the first vote of his life. "There were elections under King Faisal, but that was controlled by the British."

Bazzi and hundreds of Iraqi men and women, many of the women clad in black, head-to-toe robes, lined up at a Baghdad polling place and gratefully sipped ice water offered by election workers.

Once formed, the parliament will approve budgets, ratify treaties, question ministers and share legislative powers with the ruling 21-member Revolutionary Command Council, headed by President Saddam Hussein.

Western analysts said the Revolutionary Command Council will remain the real power center in Baghdad.

Hussein, who also leads Iraq's largest political party, will continue to make all key decisions and Cabinet appointments with the assembly used largely for consultation, the analysts said.

Iraq's constitution, providing for elections to the legislative body, was suspended in 1958 when the monarchy was ousted by a military coup.

The current move toward democratic rule follows a long period of relative stability under the Arab Baath Socialist Party, in which oil-rich Iraq has pushed through a program of industrial development rarely matched by any other Third World country.

The elections come at a time when Iraq is experiencing border skirmishes with neighbor Iran and Iranian leader Ayatollah Ruhollah Khomeini has urged Iraqis to overthrow the Baghdad government.

The majority of Iraq's population is Shiite Moslem, a sect whose loyalty in Iran is commanded by Khomeini.

In another development today, Al Dawa, a clandestine Iraqi fundamentalist Moslem organization, claimed responsibility for yesterday's grenade attack on the British Embassy here in which three gunmen reportedly were killed.

An Al Dawa spokesman told Agence France-Presse by phone that the attack was a "punitive operation against a center of British and American plotters."