Hello.

Suppose I have 3 vlans 100,200,300. Port 24 is an uplink and is tagged for all VLANs. All other ports a switched toghether by switch chip. Some ports are untagged VLAN 100. Others are on VLAN 200. Some on VLAN 300.

All VLANs are in same subnet 192.168.1.0/24.

Now I want one port to belong to all VLANs untagged. How this can be accomplished?

I know this is not the scope of VLANing. The idea is to have vlan for users, vlan for guests and vlan for management. On one port will be an administration computer which should have access to all vlans, like in a simple local LAN. There is a router at uplink which can do ebtables to forward, but I would not want to do this on that router.

https://wiki.mikrotik.com/wiki/Manual:Interface/VLAN

Look for "Setup examples"

There is no example for my situation. Hybrid port is not applicable. InterVlan routing I want to avoid on uplink router.

What you propose to do is "impossible".
There is nothing keeping the VLANs apart other than the tag and the physical separation.
Also it is not reasonable to use a single IP subnet on multiple VLANs.

To have a port setup so that VLANs are not tagged at ingress, you must have a device attached to that port that can do VLAN tagging. For instance a server that has a NIC that supports VLAN tagging.

Isn't this be done using bridging?

/interface bridge
add name=bridge1
/interface bridge filter
add action=drop chain=forward
/interface bridge port
add bridge=bridge1 interface=vlan-100
add bridge=bridge1 interface=vlan-200
add bridge=bridge1 interface=vlan-300

Somewhere in this should be ether1 and using filter allow access to all vlans?

If my goal can not be setup, then how can be configured administration station to access all vlans? Routing thru a router is possbile, but if it fails, than access to administration vlan from a specific admin station will be lost.

Yes, that is how a routed network works. When you are really concerned about that you could install two routers in VRRP or another redundant configuration.
Of course when you have different subnets you could go through the trouble of having your admin system on a tagged port and on all the networks, but
when you have to ask about that it is probably above your current capabilities to set that up.

pe1chl, you underestimate my capabilities. I can setup vlans and tagging and have admin system on separate vlan. I can use router use VRRP. Its just I would not want to bother central router when I have to access client computers on another vlan. As I started using mikrotik a short time ago, I was asking to do such routing on Mikrotik switch which is the first in the path from admin system to LAN. On a linux box I've used ebtables.