Brahimi said he was "confident" that a government can be set up but said security in Iraq must "considerably improve" before elections happen, he said.
He spoke as April became the deadliest month for American forces since they set foot in Iraq.
U.S. warplanes and helicopter gunships firing heavy machine-guns, rockets and cannons hammered gunmen as a truce in besieged Fallujah was strained by increasingly intense battles.
Elsewhere, a 2,500-strong U.S. force massed on the outskirts of the Shiite holy Najaf for a showdown with a radical cleric, raising fears of a U.S. attack on the city that would outrage the nation's relatively pro-U.S. Shiite majority.
In other major developments:
Brahimi's proposals represented a stripped-down alternative to previous, more complicated systems for a new government, a subject that has caused sharp divisions among members of the Iraqi Governing Council and U.S. administrators.
The differences were so difficult to overcome that the United States and Iraqi leaders called in the United Nations to find a solution.
Past ideas had included expanding the 25-member Governing Council to make a body that could then create an interim government. But under the ideas outlined by Brahimi, the council would be disbanded once the June 30 target date is passed.
Brahimi said the caretaker government would be "led by a prime minister and comprising Iraqi men and women known for their honesty, integrity and competence. There will also be a president to act as head of state and two vice-presidents."
A "consultative assembly" should also be created, but not an interim legislature, said Brahimi.
"I am absolutely confident that most Iraqis want a simple solution for this interim period," he said. "You don't need a legislative body for this short period."
He called for a conference of "national dialogue" to be convened after the June 30 handover to create a "consultative assembly."
Brahimi said legislative elections set for Jan. 31 would be "the most important milestone." There is "no substitute for the legitimacy that elections provide for," he told a news conference.
The Marines called a halt to offensive operations on Friday to allow negotiations between U.S.-allied Iraqis and Fallujah representatives in an attempt to ease the violence. Gunmen in the city called a cease-fire Sunday. But Marines have been responding to guerrilla fire — and striking gunmen who appear about to attack.
A U.S. Cobra attack helicopter fired rockets and heavy machine-guns before dawn Wednesday at gunmen in the city, and A-130 gunships pounded a row of buildings from which Marines say ambushes have repeatedly been launched.
In the south, Iraqi politicians and ayatollahs tried to negotiate a solution to avert a U.S. attack on the city of Najaf, home to one of Shiite Islam's holiest shrines.
A vehemently anti-U.S. cleric, Muqtada al-Sadr, was holed up in his office in Najaf, shielded not only by gunmen but by the presence of the city's main shrine only yards away.
U.S. commanders vowed to kill or capture al-Sadr, though officials suggested they would give negotiations a chance. An envoy for the cleric said Muqtada al-Sadr has asked him to convey a set of proposals to U.S. officials, according to CBS News Reporter Lisa Barron.