WIMBLEDON, England (AP) _ Once again, the busiest man at Wimbledon is referee Alan Mills. And, once again, his biggest headache is that old Wimbledon nemesis: wet weather.

For the second straight day, showers lashed the All England Club today and the prospects for any play were uncertain. More rain was forecast through the weekend.

With the tournament now more than 100 matches behind schedule, Mills is facing the possibility of play on the middle Sunday for only the second time in tournament history.

Nearly all of Wednesday's program was washed out, with Monica Seles and Jana Novotna winning the only two matches that were completed.

Seles downed Rachel McQuillan 6-0, 6-2 in a first-round match held over from Monday, and Novotna beat Wiltrud Probst 6-4, 4-6, 6-0.

Mills' office said that only 94 matches had been completed in the first three days, while 200 would have been finished in optimal conditions.

As a result of the mounting backlog, Mills had scheduled the start of play on Centre Court and Court One for two hours earlier at noon today. Matches on the outside courts were brought forward one hour to 11 a.m.

But the steady rain meant there was no chance of play starting on time.

Both top seeds were set to play second round matches on Centre Court today. Martina Hingis was up against Olga Barabschikova, while Pete Sampras was paired against Hendrik Dreekman.

Others scheduled for action included defending champion Richard Krajicek, Goran Ivanisevic and Boris Becker among the men, and Mary Pierce, Venus Williams, Iva Majoli and Anna Kournikova among the women.

Mills said he wasn't considering drastic measures _ yet.

``The problem will increase if the weather continues being bad, and the forecast for the next two or three days is horrendous,'' he said. ``The big problem comes if the weather is bad next week.

``Then we might have to make the players play singles and doubles on the same day, or play singles every day rather than having a rest day between matches.''

Mills said he is reluctant to schedule matches on the middle Sunday _ a break of tradition that occurred only once before in the 127-year history of Wimbledon. That was in 1991 after the wettest first week ever.

That day was dubbed ``People's Sunday'' and was a huge hit with common fans who got in for free. But Wimbledon officials say it would pose huge logisitical and organizational problems to try to repeat the experiment.

``The club have previously said they wouldn't want to play on the middle Sunday,'' said chief inspector Philip Coates, who is in charge of the police operation at Wimbledon. ``And when it happened in 1991, it caused so many problems that the general view was we didn't want to do it again.''

But the Merton Council, which governs the area that includes the All England Club, said it wouldn't object to the idea.

``Wimbledon is the most prestigious tournament in the world, a great boost for Merton, and we wouldn't do anything to obstruct it,'' council spokesman Paul Parry said.

The final decision would be up to club chairman John Curry and his committee. Six years ago, they waited until the Friday evening before deciding to go with Sunday play.

There's also the prospect of the tournament being extended into a third week. That has happened several times recently, including last year when the semifinals and finals of the women's doubles were held on the third Monday.

All of which revived the issue of why Wimbledon doesn't install a retractable roof on one of its stadium courts.

``It's grass, it's open air and that's the way it is,'' an All England club spokesman, Johnny Perkins, said. ``I would have thought they wouldn't just put one on only one court, and I don't think putting one on Centre Court has ever seriously been considered.''