Schools should be free to select some or all pupils by ability, said the Tory leader as he promised his party's support to fight off challenges to the remaining 164 grammars.
Mr Hague's comments, made during a visit to a London school that selects a quarter of its pupils by ability, echo his predecessor John Major's pledge to create a grammar in every town, a policy that was later abandoned. He insisted that parents should decide on school admissions procedures.
Government sources said that Conservative policy on the matter was "totally confused".
Opponents of grammar schools began collecting signatures for petitions in five areas this week, the first step towards triggering ballots of parents on the future of grammars in these areas.
Mr Hague told a group of sixth formers at Graveney School in Tooting, south London: "We have got to encourage different kinds of schools. We have got to encourage diversity.
"This school had taken the opportunity to be different from other schools. It's partially selective. Schools should be given the right to do that if that is what teachers, governors and local people want."
The Schools Adjudicator, set up by the Government to resolve disputes over admissions, cut the proportion of children selected by ability at Graveney from half to a quarter in a landmark ruling last month.
Mr Hague, who was educated at a state comprehensive, condemned the decision and attacked the Government for allowing parents to threaten the future of fully selective grammar schools. "You don't raise the average in education by destroying the best, which is what the Government is now embarking on," he said.
Mr Hague was launching an excellence in education task force to help pro-grammar school campaigners to fight off the challenge from anti- selection activists.
The campaign to remove the last grammar schools began this week in Barnet, north London; Ripon, in north Yorkshire; Sutton, south London; Trafford in Greater Manchester; and Kent.
The National Union of Teachers, the biggest teaching union, attacked Mr Hague's comments. Doug McAvoy, the union's general secretary, said: "The same offer was made by John Major and parents did not rush to take it up because they wanted their children given the widest opportunities, not scrapped at 11."
Margaret Tulloch, of the Campaign for State Education, said: "I suppose he thinks that bringing back grammar schools in areas which are comprehensive is a good policy. I thought Mr Major lost on that one."
Graveney school was opened specially yesterday for Mr Hague's half-hour meeting and photocall with sixth formers.
The teenagers were, however, sceptical about his performance. "He has not got much charisma, has he?" said Asad Khan, one of the group. Another student, Edward Wallace, who plans to study maths at Cambridge, said: "It's admirable that Mr Hague is coming to schools, but if he does not give us a straight answer we will not be convinced. He did not inspire us."Reuse content