LONDON, SEPT. 9 -- Twenty-five British soccer fans were extradited to Belgium today to face manslaughter charges stemming from the 1985 riot at Heysel Stadium in Brussels that left 39 people dead.

The Britons, most of them in their early 20s, were taken in handcuffs this morning from London's Wormwood Scrubs prison, where they have been held for the past two months. Traveling in closed police vans, they were driven 60 miles to an Air Force base in Oxfordshire, where they were turned over to armed Belgian police and placed aboard a Belgian military transport plane.

The mass extradition is unprecedented in either country, both because of the number of defendants and the nature of the charge. A total of 26 Britons were charged. One, however, remained behind pending the resolution of an unrelated case in Liverpool.

Arraigned this afternoon in a Brussels courtroom, the prisoners were transferred to Louvain prison, about 20 miles from the Belgian capital. Their trial, before a three-judge panel, is not expected to begin before the end of the year.

The extraditions came after several months of legal appeals failed to persuade British courts and Home Secretary Douglas Hurd that the defendants would get an unfair trial in Belgium, and might be in some danger in prison there.

Inmates in two other Belgian prisons rioted over the weekend in protest against what they said were special accommodations being prepared for the British prisoners. The Britons will occupy a newly remodeled wing at the Louvain institution, in apartments with bedrooms and sitting rooms.

Hurd said in a statement yesterday that he was "satisfied with the Belgian legal system and the arrangements being made by Belgian authorities."

But Eric Heffer, an opposition Labor Party member of Parliament from Liverpool, where most of the men live, said today that their trial "should have been held in this country, because of the atmosphere that has been developing in Belgium."

Heffer and lawyers for the 25 have argued that Belgian public opinion already has convicted the Britons. They cited reports today in a popular Brussels newspaper, La Derniere Heure, headlined in English: "Welcome in Belgium, Red Animals."

In a front-page editorial, the newspaper said: "The simple fact that these . . . hooligans have been extradited by the authorities of a country which jealously guards its independence is surely enough condemnation already. Throughout Great Britain, they are called the red animals, often red with the blood of others."

The May 29, 1985, riot took place during a European Cup final between the Liverpool team and Italian champions Juventus.

Evidence for the Belgian case was gathered by British police, who identified the defendants from videotape filmed during the riot. It allegedly showed them fighting, throwing missiles and causing panic among the Juventus fans that led to hundreds being trampled. Most of the dead were Italians.

For purposes of the Belgian extradition request, the 26 Britons were charged with a single count of manslaughter. That charge could be expanded, however, to include responsibility for all 39 dead. In some cases, charges could be reduced.

In an unsuccessful appeal, British lawyers argued that the extradition ought to be postponed until the charges were clarified. The lawyers also have argued that inadequate Belgian security preparation for the match and weak police supervision were equally responsible for the deaths, and have said the Britons are being made "scapegoats."

Two Belgian police officials in charge of stadium security the night of the match and the secretary general of the Belgian soccer association also have been charged in connection with the 1985 deaths.

Criticism of Belgian prison conditions last week led Belgian Justice Minister Jean Gol to take journalists on a tour of the facilities at Louvain.

Television pictures of the tour enraged prisoners at two other Belgian prisons, who then rioted for two nights.