The D.C. constitutional convention, now more than a third of the way through its 90-day session, begins public hearings next week on its proposed state constitution with some convention delegates concerned that they may not be able to complete the document on time.

Much of the first 30 days of the convention was consumed by procedural maneuvering. Few position papers or specific articles were drafted at committee level, and several delegates are saying privately there may not be enough momentum to finish the document by the May 29 deadline.

"I'm concerned," said Ward 5 delegate Talmadge Ward, one of the more vocal critics of what he calls the "sham of Saturday"--a reference to the convention's regular Saturday sessions, which often bog down in parliamentary nitpicking or shouting matches between delegates.

But convention president Charles I. Cassell expressed optimism, saying, "We have time, and we are going to write a good document."

The convention's enabling legislation, enacted by the City Council last year, calls for the 45 delegates to write a constitution in 90 days on a slim, $150,000 budget. The convention could seek an extension of time, but Cassell has indicated he does not want it and District Building sources say neither the City Council nor Mayor Marion Barry is interested.

The convention officially began March 1, but was not fully staffed and equipped at its headquarters in the old Pepco building, at Ninth and E streets NW, until well into the month.

One convention committee has adopted a preamble for the constitution and another has approved a unicameral, or single-house, legislature for the proposed state. Little other formal action has been taken. Some committee chairmen have indicated, however, that they prefer to wait until after the public hearings to draft formal articles.

Much of the committee work so far has entailed round-table discussions with experts in various constitutional fields, as delegates begin to shape their concepts about the proposed state government.

But Moore, a retired military officer, says, "We've got to stop relying on the experts at some point and come to grips with reality and write this thing."

The public hearings are to take place over a two-week period starting April 5, with most of the convention's 10 substantive committees having two sessions each.

The hearings, at which both experts and members of the general public may testify, will cover a broad cross-section of constitutional provisions, including the shape of the executive, legislative and judicial branches of the new government, its taxing authority, suffrage, regulation of utilities and the new state's relationship to the federal government.

Once the constitution is written it must be submitted to the voters of the District, probably in this fall's election. If approved at the polls it goes to Congress, where a simple majority of both the House and the Senate must approve it before statehood can be realized.