VANDENBERG AIR FORCE BASE, Calif. (AP) -- A rocket carrying a top-secret payload blasted off Tuesday from the California coast.

The Delta IV rocket lifted off at 4:12 p.m. From the Vandenberg Air Force Base, about 130 miles northwest of L. A. .

"We've just seen the successful liftoff" of the rocket, launch commentator Don Spencer asserted in a webcast.

Since the launch concerned a classified cargo for the Nation's Reconnaissance Office, no details were immediately available about whether it was boosted to its intended orbit.

The reconnaissance office, which controls the state's constellation of spy satellites, has kept mum about the purpose of the mission and directed United Launch Coalition to chop off the live broadcast three minutes after liftoff.

Intelligence analysts assume the rocket carried a radar imaging satellite capable of seeing at night and thru bad weather. Recently, the US has worked to curtail its fleet of older, heavier radar reconnaissance satellites with smaller but similarly capable ones, expounded Charles Vick, a space policy analyst with the Globalsecurity.org brains trust.

Such radar satellites would be in a position to zero in on states of interest and see details that typical Earth satellites can't, professionals announced.

Tuesday's launch concerned reconfiguring the rocket to add on 2 strap-on boosters to provide more thrust. The protecting nose cone enclosing the payload also needed to be made larger.

ULA, the joint venture of rocket builders Lockheed Martin Corp. And Boeing Company, expounded it was actually the first time the Delta IV had been launched this way.

The launch got delayed almost a week as engineers worked to mend a problem with the upper stage engine.

The following launch out of Vandenberg will be a flight test of the Minuteman III on April 10.