Attorneys, educators and congressional aides agreed yesterday that the Supreme Court's ruling upholding a Minnesota tax deduction law will give new vigor to tax credit proposals like the Reagan administration's, which the Senate Finance Committee approved in May.

Sen. Robert J. Dole (R-Kan.), chairman of that committee, hailed the decision as "good news for millions of American parents who bear the double burden of public school taxes and private school tuition . . . . The court wisely recognized the strong public interest in assuring the continued financial health of private schools, the public benefits possible with private education and the importance of . . . wholesome competition and diversity . . . ."

But, other observers said, by stripping away the curtain of constitutional arguments, the decision also may prompt greater scrutiny of the proposal's cost, particularly since the Minnesota law offers tax deductions to parents of both private and public school students.

Perhaps for that reason, the hosannas from some advocates of tuition tax credits were muted. Monsignor Daniel F. Hoye, general secretary of the United States Catholic Conference, said, "The USCC welcomes the decision of the Supreme Court in the Minnesota tuition tax deduction case . . . .

"Certainly, at the very least, this decision should be a message to Congress that such tax relief measures to help parents educate their children are not de facto unconstitutional," he added.

Sen. Daniel Patrick Moynihan (D-N.Y.), a longtime supporter of tuition tax credits, said in a prepared statement, "This decision is good news. Those of us who have supported tuition tax credits . . . have always assumed them to be constitutional . . . .

"The Supreme Court decision is not, as such, an argument either for or against tuition tax credits," Moynihan added. "It is simply a statement that this is an issue of public policy that may be decided free of any constitutional constraints."

The Congressional Budget Office has put a $2.8 billion five-year price tag on the Reagan administration's bill, which, after a two-year phase-in period, would offer a credit of $300 per child to taxpayers who paid at least $600 in tuition for that child. Families with incomes above $40,000 would get proportionately smaller credits; families with incomes above $50,000 would get nothing.

If amended to add public school students, who outnumber their private school counterparts eight to one, the measure's price tag would inevitably increase.

Education Secretary T.H. Bell, in a telephone interview from California, said last night that such a cost increase might dissuade the administration from amending its bill to conform with the Minnesota law.

He also objected to the congressional estimates of revenue loss, saying that they more than double administration projections. The cost of the bill in its current form, he added, is too small to overshadow policy considerations.

The tuition tax credits have long been an odd-bedfellow issue, cutting across political, religious and demographic lines. President Reagan has spoken out in favor of it on numerous occasions. The 1980 Democratic Party platform also supported "constitutionally acceptable" tax relief for parents of pupils in nondiscriminatory private schools.

Religious educators, from orthodox Jews to evangelical Christians, expressed satisfaction with the court decision.

Meanwhile, the often-feuding teachers' unions, the National Education Association and the American Federation of Teachers, both greeted the news with warnings that tuition tax credits would imperil any push for educational excellence. Both groups renewed their pledges to fight the administration's proposal.

"No green light has been given by the Minnesota case" to Congress and the state legislatures, said Thomas A. Shannon, executive director of the National Association of School Boards. "The most you can say is that it's a flashing yellow."

Among the chief beneficiaries of federal or state tuition tax credit legislation, according to Robert Smith of the Council on American Private Education, would be hundreds of thousands of urban, blue-collar ethnic families in the industrial North and Midwest who send their children to parochial school.