Maryland Attorney General Stephen H. Sachs, unveiling an ambitious but politically risky proposal that he called the "centerpiece" of his Democratic gubernatorial campaign, advocated yesterday an increase in aid to public education of $250 million a year, to be financed by a 1-cent increase in the state's sales tax.

Sachs, already trailing badly in public surveys behind his Democratic opponent, Baltimore Mayor William Donald Schaefer, conceded that his proposal to increase the sales tax to 6 cents would be "controversial" but said it is necessary to end a "crisis" in the state's public schools.

"No politician, especially one running for governor, likes to propose a tax increase," said Sachs as he floated the proposal and a 29-page position paper on education at press conferences in Greenbelt and Baltimore. "I do so because I am convinced this increase is necessary to prevent a crisis facing Maryland . . . . Not to tell that truth is to mislead the people . . . . "

Sachs predicted that his plan would be met with initial criticism, but said he would turn the months remaining before the Sept. 9 gubernatorial primary into a referendum on the issue that would turn up considerable public support for the first sales tax increase in almost a decade.

"I believe after a spring and summer of discussion and reflection, as autumn comes upon us and back-to-school days draw near, that my fellow Marylanders will come to see this proposal for what it truly is," said Sachs. "It is a penny for excellence, it is a penny for high standards, it is a penny for our futures, it is a penny for our children."

As predicted, Sachs' proposal drew immediate fire from Schaefer and from legislative leaders in Annapolis, who are wrestling with a similarly controversial, though less expensive, plan to increase education aid sponsored by House Speaker Benjamin L. Cardin (D-Baltimore).

"The growth rate of our revenues is adequate to handle a progressive education formula," said Cardin. "I'm sympathetic to what he is trying to accomplish, but we don't need a tax increase."

Schaefer also criticized Sachs' sales tax proposal, which would finance an education plan costing $753 million more over five years than the one backed by the mayor and Cardin.

"There's enough money to fund [an education increase] right now," said Schaefer. "To call for a tax increase, that isn't the answer."

Several Prince George's County school board members who attended Sachs' announcement yesterday praised the proposal.

"The plan looks fine at first glance," said Barbara F. Martin. "What impressed me is that he had nerve enough to mention a tax increase in an election year."

Sachs, stressing that Maryland ranks seventh in the nation in wealth but 35th in spending on public education, tied an increase in education aid to a range of problems facing the state, including economic development, the ability to attract and retain qualified teachers, the high school dropout rate, and alcohol and drug abuse among the young.

The elements of Sachs' $250 million education proposal include:

*A $150 million increase in state aid to be used solely to boost teacher salaries and benefits. Of the $125 million going to teachers' salaries, $120 million would be distributed under the existing "wealth-based" formula that benefits poorer jurisdictions the most. The remaining $5 million would be allocated among urban and suburban jurisdictions based on a "cost of education" index on the theory that areas like Montgomery County have a higher cost of living.

*A $16 million program to finance prekindergarten classes for about 16,000 economically disadvantaged 4-year-olds in 470 elementary schools in poor districts. Sachs said a complete prekindergarten program would give poor children who "frequently come to school fatally and permanently behind" a chance to begin school on an equal basis with their more affluent peers.

*A $14 million jobs program for high school graduates meeting certain grade, attendance and behavior standards. Under this program, the state would pay half the minimum-wage salaries of such youths for one year, with jobs and salary balances supplied by the private sector. The purpose, said Sachs, is to "make young people understand the link between school performance and jobs, give them incentives to stay in school and help reduce the alarming dropout rate." This "Job Chance" program would also include creation of a state commission to design and oversee the plan.

*A $20 million grants program for local jurisdictions "to develop creative, innovative approaches" to education. The program, which would be competitive but fund pilot projects throughout the state, would help stimulate what Sachs called "ferment" in the areas of innovative curriculum, preparing students for the job market, combating such problems as truancy, teen-age pregnancy and substance abuse, and professional development and recruitment of teachers.

*A $50 million increase in aid to higher education, the details of which Sachs said he would outline later.

Sachs, defending his plan to increase the sales tax, said new revenues would be needed because budget cuts at the federal level will impose additional burdens on state governments for programs such as revenue sharing and mass transit.

He also said that a sales tax increase would be less regressive than an increase in the state income tax because food and some other necessities are exempt from the sales tax and because Maryland residents pay, per capita, a relatively low amount in sales tax compared to residents of other states.

According to Sachs, a family of four with an annual income of $17,500 would pay an additional $36 a year under his proposal. A similar family with an income of $47,500 would pay $74 more.

Despite expressing confidence his proposal will meet with public acceptance, Sachs predicted yesterday it will be dubbed the "Sachs tax."

Increasing the sales tax to benefit education is not a novel idea, having been used in at least one other state. Arkansas Gov. Bill Clinton (D) pushed an increase through that state's legislature in 1983 and was easily reelected in 1984.

But Sachs is bucking local political history in proposing a tax increase just before an election. When former Maryland Gov. William Preston Lane pushed through the state's first sales tax more than 35 years ago, he was vilified when he ran for reelection as voters frequently hurled pennies at him. He lost his 1950 bid for reelection.

And a number of politicians in Annapolis yesterday compared Sachs' proposal to Walter Mondale's disastrous suggestion for a tax increase in 1984, when the Democratic presidential nominee was swept under by the Reagan landslide.