Prime Minister Tony Blair's Labor government on Thursday published long-awaited details of its plans to overhaul British higher education by, among other things, allowing universities in England and Wales to charge tuition fees of up to $5,450 per year.

Some of the most vocal opponents of the legislation, which was first announced last January and formally presented in November, have come from the Labor Party's own ranks. Many Labor members of Parliament argue that the imposition of the "top-up fees" would price higher education out of the reach of financially needy students and make universities more elitist.

More than 150 Laborites in Parliament have signed a petition objecting to variable fees, which they say would produce a two-tier system by allowing universities like Oxford and Cambridge to charge higher fees than less-prestigious institutions could command. The dissenters recommended instead that a $4,550 flat fee be imposed at all universities, but the Blair government rejected that idea, and the education secretary, Charles Clarke, said that the variable-fee provision was not negotiable.

Moreover, he said on Thursday on the floor of the House of Commons, "no student from a poor background will be worse off as a result of our proposals."

The new tuition structure would take effect in 2006. University students in England and Wales now pay a flat, upfront fee of $2,050, and nearly half receive financial aid that covers the entire amount.

Under the government's plans, the new fees would be charged only after students had graduated and their annual income exceeded $27,300. Students from the poorest families would receive aid of up to $5,450 a year, the full amount of the fees, derived from subsidies, grants, and scholarships. Low-interest student loans of up to $7,300 would also be introduced, and all student loans and fee debts would be written off after 25 years.

The proposed fees are relatively low by American standards, and university administrators here support the legislation almost unanimously. The additional revenue would pay for better libraries, laboratories, and technology, and would help universities attract better professors with higher salaries, said Ivor Crewe, head of Universities UK, an association of vice chancellors that supports the proposals.

But the measures have prompted outrage from all sides of the political spectrum, and Prime Minister Blair has made the bill's passage a testing point for his government. "This is a reform that is absolutely central to the future of Britain and the future of the British economy," he said at a news conference last month. "If we want people to be better educated and more people to go to university ... we have got to find a fair method of funding it. You cannot widen access, increase the amount of money going to universities, unless we have a balance between what the state pays and what graduates pay upon graduation, and that is the only fair choice for people."

In addition to the revolt within Mr. Blair's own party, which some political analysts believe could threaten the survival of his government, the proposals face attacks from the opposition Liberal Democrats and Conservatives. Tim Yeo, the Conservative Party's chief spokesman on education issues, has said that the debt burden that students would face, if the Blair plans were enacted, would deter many from pursuing a higher education.

Mr. Yeo denounced the proposals as a "politically correct" attempt to legislate accessibility to higher education. "The main reason top-up fees are necessary is that Tony Blair set a target of 50 percent of young people to go to university, and this is the only way for that target to be imposed," he said. "Employers are not saying that they need more graduates. Universities aren't saying they need more people with fewer academic qualifications. What we need is more vocational training."

Student groups are equally opposed to the Blair government's plans, if for very different reasons than the Tories. Students recognize that a university education is costly and that they should bear some of that expense. But the imposition of the new fees would simply result in a more unequal system, said the president of the National Union of Students, Mandy Telford.

"Top-up fees will create a marketplace in higher education where you can essentially buy your degrees," Ms. Telford said. "Students from poorer backgrounds are already put off going to school by debt or fear of debt, and this will just make that worse." Ms. Telford's group will lobby members of Parliament over the next several weeks as the bill is debated in the House of Commons. A vote is expected around the end of the month.