Intel worked on a 64-bit extension to the Pentium prior to developing the Itanium, but the this article does not indicate any details of the Intel design. AMD64 wasn't publicly announced until 1999, so I suspect that this is not the design the OP remembers.
From What’s Up With Willamette? (Part 1) (the Wikipedia article on the Itanium links to this article):
In early 1993 Intel’s Santa Clara processor design team had just finished off the P5 project (Pentium) and started work on the P7. . . . The P7 was a powerful 64-bit x86 compatible successor to the P6 envisioned to have around 20 million transistors or nearly four times as many as the Pentium Pro. In some ways Intel’s original P7 project conceptually resembles AMD’s K8 “sledgehammer”, the 64-bit successor to the K7 Athlon.
The P7 progressed only far along enough for Intel’s engineers to realize that extending x86 to 64 bits, and staying competitive with RISC processors, would be challenging to say the least. . . . In 1994 the Santa Clara team dropped all work on the 64 bit x86 processor design called P7 and started on the first implementation of the new IA-64 architecture arising from the Intel-HP alliance, a processor later known as Merced.
