Comcast Corp. will become the first major cable TV operator to roll out wireless broadband outside of Wi-Fi hotspots as it launches the service in Portland, Ore., on Tuesday, with at least three other cities to follow this year.

Comcast will offer speeds of up to 4 Megabits per second, faster than any other comparable, non-Wi-Fi service currently being marketed. The service is for use with laptops, but not other mobile devices.

Comcast’s wireless broadband, which lets users surf the Web on the go with their computers, pits it squarely against the mobile data offerings of phone companies.

But the cable operator is coming out first with the market’s fastest wireless broadband, using WiMax technology. Phone companies have lined up behind a competing technology called LTE, with Verizon Communications Inc. planning to deploy it next year.