WASHINGTON – Senate Democratic leader Harry Reid prepared to unveil long-awaited healthcare overhaul legislation on Wednesday, with the first test vote on the package expected by the end of the week.

The healthcare reform bill, President Barack Obama's top domestic priority, has been delayed in the Senate for weeks as Reid waited for cost estimates and searched for an approach that can win the 60 votes needed to overcome Republican procedural hurdles.

Senate Democrats have scheduled a 5 p.m. EST meeting in which Reid will brief them on the bill, and on the cost estimates provided by the nonpartisan Congressional Budget Office.

The bill's release would clear the way for a vote on Friday or Saturday by the full chamber on whether to proceed to debate on the measure — the first key procedural hurdle for the Senate plan.

The measure, which merges two healthcare measures passed by Senate committees, would expand insurance coverage to tens of millions of uninsured people and offer subsidies to help low-income Americans pay for it.

Democrats have no margin for error — they control exactly 60 seats in the 100-member Senate — and some moderate Democrats have rebelled at Reid's decision to include a new government-run public insurance program in the bill.

The House of Representatives already has approved a similar measure. If the Senate passes its bill, differences in the two measures would have to be reconciled before the final versions can be voted on again in both houses and, if passed, sent to the president for his signature.