ANCHORAGE, Alaska (AP) _ Tom Williams says he really didn't expect to end up on Phil Donahue's national television show when he came up with his ''mail-order bride'' idea a couple of months back.

''I stuck a $27.50 ad in the paper to provide women for my men,'' said Williams, who is building a replica 1800s mining camp as a tourist attraction at Paystreke, 80 miles south of Anchorage.

The ad appeared in September. Then TV networks, magazines and the wire services had stories about Williams and the men at Paystreke. Donahue featured him last week.

''It backfired, I guess,'' Williams said Tuesday at a news conference he called to announce his engagement to Jill Bandock, one of hundreds of women who answered the call for brides.

Backfired? Williams has received the kind of free publicity that Madison Avenue advertising men dream about. People from all over the country are calling to reserve hotel rooms that haven't been built yet. He has scrapped plans to build a 100-room hotel by 1987 - now it's a 300-room hotel, to be finished by next July.

''Well, it's a good backfire,'' Williams allowed. ''We feel like we should go along with it.'' But, he added, ''If it becomes a nuisance, and it interferes with my business or personal life ... then there won't be any more interviews.''

Bandock, 22, of Olympia, Wash., arrived at Paystreke less than three weeks ago. She found an unfinished collection of buildings with no running water, electricity or telephones. She also found Williams, 40, a bear of a man who sports a bushy beard and an oversized Bowie knife on his hip.

''My instincts tell me it's the right decision,'' Bandock said Tuesday. ''I decided yes, this is the man I'd like to spend the rest of my life with.''

Williams had proposed last week on the Donahue show, but Bandock declined, saying it wasn't the proper time. Tuesday morning, at an Anchorage diner, ''She looked at me and said, 'Yes,''' Williams said.

''I said, 'Yes, what?' And she said, 'Yes, I'll marry you 3/8'''

The wedding is set for next September, so it won't interfere with preparations for the hectic tourist season expected next summer, he said. ''The business this year is a priority item.''

Bandock agreed. ''I'd like to get out there and pound some nails along with the men - help put the town together,'' she said.

When wedding bells finally do ring, it will be at Paystreke, of course. And, yes, the news media will be invited. ''Hey, if it weren't for you guys, none of this would have happened,'' Williams said.

Which drew the question: Was the mail-order bride appeal nothing more than an elaborate publicity stunt?

Perhaps, Williams said. But he said it was reporters, not he, who decided the story fit the great Alaskan image of rugged men, mail-order brides and rustic mining camps. ''Whose publicity stunt is it - the media's or ours?''