Monday night's meeting of the joint policy committee, attended among others by Margaret Beckett, the acting leader, and Harriet Harman, the party's Treasury spokeswoman, ruled out an amendment to a white paper on education reform.
While the unamended paper identifies nursery education as a key plank of future policy, the decision against including a timescale could provoke a row today when it reaches the party's ruling National Executive Committee, with some members arguing that such a critical feature should be elevated into a more specific commitment.
The amendment was tabled a fortnight ago by the National Policy Forum, which includes representatives from trade unions and constituencies.
John Patten, Secretary of State for Education, quickly seized on the open-ended nature of the pledge as evidence of Labour making promises while failing to attach the price tag - in this instance, about pounds 900m a year.
However, Mrs Beckett made clear yesterday that John Smith's rule that no such commitments should be made at this stage of a Parliament has prevailed.
Ann Taylor, the party's education spokeswoman, who wrote the paper, was likewise lukewarm over the five-year timescale, believing it would never gain approval.
Ms Taylor circulated a note to all three leadership candidates yesterday emphasising that the document included no such pledge. Other Labour sources pointed out that the party's recent local-election gains, such as Kent, were already bringing about increased provision.
The paper promises an inquiry into the best replacement for 'simplistic' league tables, the replacement of the current testing system with assessments that have the 'confidence of parents and teachers alike', the abolition of the assisted places scheme and replacement of A-levels with a new General Certificate of Further Education, an examination for 16- to 19-year-olds embracing academic and vocational courses.
The paper also uses a more ambivalent tone in relation to grant-maintained schools, adopting the circuitous route of a funding vacuum to reach the aim of their eventual demise, rather than stating that they would be 'abolished' as such.
A Labour aide said the intention was not to 'automatically abolish' grant-maintained schools - although no new ones would be allowed. The idea was to 'induce those schools back into full local authority involvement as swiftly as that can be achieved'.Reuse content