Pre-orders for Apple’s (AAPL) tablet computer held steady a week before its April 3 release.

According to an update posted Friday morning — two weeks to the day after Apple began accepting online orders — an estimated 240,000 iPads had been pre-ordered for delivery.

Daniel Tello, who has been tracking order numbers submitted by volunteers, notes that this does not include iPads reserved for pick-up at Apple Stores, which the Boy Genius reports were pouring in the first weekend at the same rate as pre-orders. Nor does it include bulk orders by schools and businesses.

Speaking strictly about the pre-orders he tracks, Tello says a bookie might take odds at 300,000 units by April 3. “But the conservative in me,” he says, “would bet under. About 280k would be my safe prediction.”

At an average selling price of $640 per iPad, 280,000 units would yield nearly $180 million in gross revenue.

Tello summarizes the first two weeks pre-orders as follows:

• 120,000 units on first day
• 70,000 units (6 days at 12,000 units/day) over the first week, excluding Day 1
• 50,000 units (7 days at 7,000 units/day) over second week

Note: Unit numbers are calculated by subtracting average daily non-iPad orders and multiplying the difference by the average number of iPads per order. For more on Tello’s methodology, see his blog, Deagol’s AAPL Model.

Tello and his colleagues at Investor Village’s AAPL Sanity board continue to track iPad pre-orders. If you want to contribute to their spreadsheet, send the data to ipadsales10@gmail.com. Include your order number with the last three digits Xed out, the number of iPads you ordered, the order time, time zone, memory capacity and whether your iPad is Wi-Fi only or Wi-Fi + 3G.

See also:

• iPad week 1: 190,000 pre-orders
• iPad pre-orders: 10,000 per day
• Apple orders drop sharply
• Day 1 estimate: 120,000 iPad sales
• Apple sells 50,000 iPads in two hours
• The wild iPad Ruckus begins
• How many iPads will Apple sell?

[Follow Philip Elmer-DeWitt on Twitter @philiped]