Thanks for your suggestions Andrew, Roland and Jason.  Here's what I found:

1) ifconfig blah blah blah media 10BaseT/UTP .. doesn't work ..
   and nor does .. 10baseT/UTP, 10baseT, UTP .. etc.  The response is
   always: ifconfig: SIOCSIFMEDIA: Device not configured

2) Depending on the machine, the time of day (network traffic?), etc. .. the
   card with a cable in its UTP port is auto-detected as 10base5/AUI or
   10base2/BNC.  Either way, it takes several minutes for an address to be
   assigned by DHCP - and the connection is unreliable - requiring an
   'ifconfig we1 down'/ 'ifconfig we1 up' sequence to make it go again.
   I have RedHat Linux 5.1 on another partition on this machine - and it
   correctly recognises the UTP connection and works without trauma.

3) Jason - I didn't understand your comment about autoselection. Does the
   kernel have a separate driver for SMC-Ultra - and is there some way I
   can force use of that instead?  Or perhaps the kernel could be modified
   to try an SMC-Ultra first?

4) Outputs from 'dmesg' and 'ifconfig' are attached.  Andrew, I hope they
   are helpful.

G.
--

All rights reserved.

NetBSD 1.3.3 (GENERIC) #0: Fri Dec 11 16:21:49 PST 1998
    root@struis:/usr/src/sys/arch/i386/compile/GENERIC
cpu0: family 4 model 3 step 5
cpu0: Intel 486DX2 (486-class)
real mem  = 16379904
avail mem = 13512704
using 225 buffers containing 921600 bytes of memory
mainbus0 (root)
isa0 at mainbus0
com0 at isa0 port 0x3f8-0x3ff irq 4: ns16550a, working fifo
com1 at isa0 port 0x2f8-0x2ff irq 3: ns16550a, working fifo
lpt0 at isa0 port 0x378-0x37b irq 7
wdc0 at isa0 port 0x1f0-0x1f7 irq 14
atapibus0 at wdc0
wd0 at wdc0 drive 0: <Conner Peripherals 425MB - CFS425A>
wd0: using 16-sector 16-bit pio transfers, chs mode
wd0: 406MB, 839 cyl, 16 head, 62 sec, 512 bytes/sec
we1 at isa0 port 0x300-0x31f iomem 0xcc000-0xcffff irq 10
we1: SMC8216/SMC8216C Ethernet (16-bit)
we1: Ethernet address 00:00:c0:24:a8:9e
npx0 at isa0 port 0xf0-0xff: using exception 16
pcprobe: reset error 4
pc0 at isa0 port 0x60-0x6f irq 1: color
pc0: console
fdc0 at isa0 port 0x3f0-0x3f7 irq 6 drq 2
fd0 at fdc0 drive 0: 1.44MB, 80 cyl, 2 head, 18 sec
biomask 4040 netmask 4440 ttymask 44c2
WARNING: Disk appears to be old-NetBSD or FreeBSD.  See installboot(8).
boot device: wd0
root on wd0a dumps on wd0b
root file system type: ffs
syncing disks... 8 8 6 4 done
Copyright (c) 1996, 1997, 1998
    The NetBSD Foundation, Inc.  All rights reserved.
Copyright (c) 1982, 1986, 1989, 1991, 1993
    The Regents of the University of California.  All rights reserved.

NetBSD 1.3.3 (GENERIC) #0: Fri Dec 11 16:21:49 PST 1998
    root@struis:/usr/src/sys/arch/i386/compile/GENERIC
cpu0: family 4 model 3 step 5
cpu0: Intel 486DX2 (486-class)
real mem  = 16379904
avail mem = 13512704
using 225 buffers containing 921600 bytes of memory
mainbus0 (root)
isa0 at mainbus0
com0 at isa0 port 0x3f8-0x3ff irq 4: ns16550a, working fifo
com1 at isa0 port 0x2f8-0x2ff irq 3: ns16550a, working fifo
lpt0 at isa0 port 0x378-0x37b irq 7
wdc0 at isa0 port 0x1f0-0x1f7 irq 14
atapibus0 at wdc0
wd0 at wdc0 drive 0: <Conner Peripherals 425MB - CFS425A>
wd0: u\M^?sector 16-bit pio transfers, chs mode
wd0: 406MB, 839 cyl, 16 head, 62 sec, 512 bytes/sec
we1 at isa0 port 0x300-0x31f iomem 0xcc000-0xcffff irq 10
we1: SMC8216/SMC8216C Ethernet (16-bit)
we1: Ethernet address 00:00:c0:24:a8:9e
npx0 at isa0 port 0xf0-0xff: using exception 16
pcprobe: reset error 4
pc0 at isa0 port 0x60-0x6f irq 1: color
pc0: console
fdc0 at isa0 port 0x3f0-0x3f7 irq 6 drq 2
fd0 at fdc0 drive 0: 1.44MB, 80 cyl, 2 head, 18 sec
biomask 4040 netmask 4440 ttymask 44c2
WARNING: Disk appears to be old-NetBSD or FreeBSD.  See installboot(8).
boot device: wd0
root on wd0a dumps on wd0b
root file system type: ffs
Copyright (c) 1996, 1997, 1998
    The NetBSD Foundation, Inc.  All rights reserved.
Copyright (c) 1982, 1986, 1989, 1991, 1993
    The Regents of the University of California.  All rights reserved.

NetBSD 1.3.3 (GENERIC) #0: Fri Dec 11 16:21:49 PST 1998
    root@struis:/usr/src/sys/arch/i386/compile/GENERIC
cpu0: family 4 model 3 step 5
cpu0: Intel 486DX2 (486-class)
real mem  = 16379904
avail mem = 13512704
using 225 buffers containing 921600 bytes of memory
mainbus0 (root)
isa0 at mainbus0
com0 at isa0 port 0x3f8-0x3ff irq 4: ns16550a, working fifo
com1 at isa0 port 0x2f8-0x2ff irq 3: ns16550a, working fifo
lpt0 at isa0 port 0x378-0x37b irq 7
wdc0 at isa0 port 0x1f0-0x1f7 irq 14
atapibus0 at wdc0
wd0 at wdc0 drive 0: <Conner Peripherals 425MB - CFS425A>
wd0: using 16-sector 16-bit pio transfers, chs mode
wd0: 406MB, 839 cyl, 16 head, 62 sec, 512 bytes/sec
we1 at isa0 port 0x300-0x31f iomem 0xcc000-0xcffff irq 10
we1: SMC8216/SMC8216C Ethernet (16-bit)
we1: Ethernet address 00:00:c0:24:a8:9e
npx0 at isa0 port 0xf0-0xff: using exception 16
pcprobe: reset error 4
pc0 at isa0 port 0x60-0x6f irq 1: color
pc0: console
fdc0 at isa0 port 0x3f0-0x3f7 irq 6 drq 2
fd0 at fdc0 drive 0: 1.44MB, 80 cyl, 2 head, 18 sec
biomask 4040 netmask 4440 ttymask 44c2
WARNING: Disk appears to be old-NetBSD or FreeBSD.  See installboot(8).
boot device: wd0
root on wd0a dumps on wd0b
root file system type: ffs
--

we1: flags=8863<UP,BROADCAST,NOTRAILERS,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	media: 10base5/AUI
	inet 172.242.36.122 netmask 0xffffff00 broadcast 255.255.255.255
--