EAST BERLIN (AP) _ Promised a share of power by the ruling Communists, East Germany's inexperienced opposition groups failed to agree today on whether to join the government they eventually hope to replace.

A leader of the opposition Social Democrats conceded that informal discussions among the numerous pro-democracy groups has yet to yield a common strategy on how closely the opposition should work with the rival Communists.

Meanwhile, East German border guards worked through the night dismantling a 325-yard stretch of the Berlin Wall. They planned to replace the section with a simple metal fence.

Communist Premier Hans Modrow offered Monday to rebuild his Cabinet to include opposition forces such as the Social Democrats and New Forum, the largest of the reform movements challenging the Communists.

Modrow called for talks Wednesday to determine which ministerial posts could be filled by reform activists, and Social Democrat leader Ibrahim Boehme agreed that swift and united action was needed to avert collapse of the East German economy.

But Ingrid Koeppe, a prominent New Forum activist, said the opposition needed time to consult with grass-roots activists and to coordinate positions of the different groups. She told The Associated Press she did not know when negotiations on an opposition role in the leadership could begin.

Ulrich Kasparech, business manager of the Social Democrats, also said further talks among the fractious new political groups are needed.

''There is no consensus yet,'' Kasparech told The AP. ''This will depend on the groups being able to come to agreement, and they have no further meetings set at this time.''

Pro-democracy protests late last year toppled the old Stalinist regime, which was replaced by reform-oriented Communists. The new regime has promised free and open elections on May 6.

But the opposition, which hopes to handily defeat the Communists in the balloting, has been split sharply over strategy and direction.

Kasparech said other reform advocates met with Boehme earlier but that the groups currently disagree about the share of Cabinet seats they should seek.

Boehme, in an interview today with the Communist Party daily Neues Deutschland, appealed to West German Social Democrats to provide immediate aid to East Germany to halt the exodus of workers fearing no change in their spartan lifestyles can be expected soon.

Nearly 2,000 East Germans per day have been fleeing to West Germany, a sign of dwindling hope for an East German recovery.

Communists currently hold 16 ministerial posts in Modrow's 27-member Cabinet, with Liberal Democrats in four, Christian Democrats with three, and two each for the National Democrats and the farmers' party.

The non-Communist Cabinet members are from officially recognized parties once aligned with the Communists.

Since the Communists were stripped in December of their constitutional guarantee of a leading role, reform groups have argued that Modrow's government lacks a political mandate and therefore is a transitional force with limited powers.

Until Monday, the groups had resisted formally joining Modrow's government, partly from fear they would share the blame for the economic mess left by 40 years of monopoly communism.

Since setting the election date in December, the regular talks between the Communists and the opposition have been mired in procedural squabbles and infighting.

In West Berlin, several hundred gathered along crowd control barriers lined up along the graffiti-splattered Berlin Wall to watch East German border guards begin dismantling the hated barrier. It is to be replaced this week by a fence.

West Berlin government spokesman Werner Kolhoff said he was informed by East Berlin officials that other segments of the wall would be removed later.

The wall was symbolically breached on Nov. 9, when East Germany scrapped travel restrictions on its citizens and began opening new border crossings to West Germany.