BALTIMORE, NOV. 26 -- A coalition of education activists said today that Maryland should spend an additional $628 million on its schools to try to ensure that students in the poorest parts of the state receive the same education as those in affluent areas.

The proposal by the Metropolitan Education Coalition would send most of the extra money to areas such as Baltimore and parts of the Eastern Shore, which have large concentrations of poor children. The state's spending per child would increase an average of $900, about 18 percent above last year's level. The state spends about $1.6 billion on elementary and secondary schools, subsidizing about 40 percent of the overall cost of public instruction in the state.

Coalition leaders said today that their financing method, if embraced by the General Assembly and Gov. William Donald Schaefer, could provide a political solution to the problem of inequitable funding of schools, an issue that has provoked lawsuits in other states.

But it is not clear that Maryland will be spared a court fight. This month, the state chapter of the American Civil Liberties Union initiated a study of Maryland's school funding formula. Maryland ACLU Executive Director Stuart Comstock-Gay said that although the group will not decide whether to file a suit for six or nine months, the shifting of money from wealthier to poorer areas "is not extremely likely to happen through legislation alone."

Whether through a legal fight or legislation, coalition leaders said the case for reallocating school aid was strengthened last week by state School Superintendent Joseph L. Shilling, who produced a new "report card" on each of Maryland's 24 school systems.

The ratings, based on standards schools are expected to meet by 1995, showed that, in general, the most affluent counties have the best student test scores and attendance rates, and the fewest dropouts.

Coalition leaders are testing their idea among legislators, looking for sponsors in the General Assembly session that starts in January. But today, Schaefer's education aide, Judy Sachwald, called it "really a serious, very constructive proposal."

Sachwald said Schaefer is unfamiliar with the proposal's details but is "willing to take a fresh look at education spending generally."

The proposal is in step with a gubernatorial commission on the state's tax structure, which is preparing to recommend an increased and expanded sales tax and a redistribution of money to poorer parts of the state.

The proposed education formula could be a blow to relatively affluent school systems, such as those in Montgomery and Howard counties. "I would assume we won't do very well," said Lois Stoner, the lobbyist for the Montgomery schools.

The coalition, formed nearly four years ago as a Baltimore-area group, contains about 300 organizations and individuals around the state.

In releasing the proposal, the coalition did not calculate how it would affect each of Maryland's 24 school systems, although leaders contend that each jurisdiction would see more money.

Tru Ginsburg, the coalition's president, portrayed the proposal as "very child-centered," because it is based on the actual cost of providing a good education to every Maryland student.

Specifically, it would update the state's basic education subsidy, giving special compensation to schools for disadvantaged and handicapped students. In addition, especially poor jurisdictions would get additional money to guarantee all children a "basic quality education."

As an appeasement to wealthier areas, the formula would disburse $17.4 million to school systems in counties with a relatively high cost of living -- including Montgomery, Prince George's and Anne Arundel counties.

The proposal also incorporates the theme, popular with Schaefer and Shilling, of holding schools "accountable." A school system would not be eligible for any additional money unless it writes a school-by-school plan for meeting the new standards Shilling and the State Board of Education have set.