In an effort to improve student performance and possibly boost sagging enrollment, the Washington School Board has decided to offer full-day kindergarten programs next fall in all the city's 128 elementary schools.

The board also voted at an acrimonious meeting Wednesday night to provide free half-day nursery classes for 4-year-olds throughout the city.

"We feel the earlier we get young people and the more we can work with them, the more success we'll have," said school Superintendent Vincent E. Reed.

The all-day kingergartens, Reed said, will have more academic substance and less play time than most kindergartens have had in the past.

Washington will be the only public school system in the area next fall that will provide full-day kindergarten for 5-year-olds, and half-day nursery classes for all 4-year-olds who enroll.

Last month, the Maryland State Board of Education voted to provide classes for 4-year-olds at 105 schools throughout the state where achievement is low.

At Wednesday's meeting, the D.C. school board also decided to:

End an unusual six-year-old arrangement under which the Hawthorne School, a small, private high school, was allowed to use an old public shcool building rent-free in return for enrolling 41 D.C. public school students without charging them tuition.

Hold hearings in May on Reed's proposal to close 23 schools because of declining enrollment.

Provide considerable public information about contract negotiations with the unions that represent teachers and other school employes, although the negotiations themselves would remain secret.

The six-hour meeting, which lasted until 1:30 a.m., was marked by bitter personal exchanges between board members and frequent taunts and jeers from the audience that jammed the room and thronged the hallways outside.

Board president Conrad P. Smith, who headed a six-vote majority on most issues, clashed repeatedly with members John Warren, Frank Shaffer-Corona and Barbara Lett Simons.

At one point, when Smith tried to quiet him, Shaffer-Corona said: "Mr. President, if you would shut your mouth and let me speak."

Later, Warren chanted, "Point of order, point of order" about 50 times after Smith recognized board member Betty Ann Kane. What Kane had to say was inaudible.

Several administrators who attend school board meetings regularly said Wednesday's session was as bitter and raucous as those that preceded the firing of superintendent Barbara Sizemore 2 1/2 years ago.

For two years after that, board meetings were relatively calm, they noted. But the meetings have become increasingly stormy since January, when Smith was elected president by a 6-to-5 vote over Simmons. Simmons and her supporters since than have frequently attacked him.

Board member R. Calvin Lockridge went home in the middle of the meeting, declaring that it had become "very painful."

Yesterday Lockridge said he had sent a letter to his colleagues urging them "not to humiliate each other" and to "stick to issues, not personalities."

Warren said he raised his frequent objections and points of order because he wanted "to make sure that (Smith) conducts the meeting right . . . and gives the public its full day in court."

Despite the acrimony, the school board voted unanimously, with only Warren abstaining, to set up full-day kindergartens and half-day prekindergartens throughout the city.

This year, about two-thirds of the schools have all-day kindergartens. In the others, they are half-day.

There are half-day nursery classes this year in 45 schools, full-day nursery classes in 46 schools and none in 37 schools.

Kane, chairman of the board's finance committee, said the variations were the result of "local choice and tradition." Next year, she said, if enrollment is below projections, some of the half-day prekindergartens may become full-day again.

Kane said an expected 5,000 drop in school enrollment next year would allow teachers to be switched from elementary grades to kindergarten without raising expenditures. But she said she hoped the full-day kindergartends would attract more students to the public schools.