With one class remaining in the Open Jumper division, McLain Ward and Hillary Dobbs are locked in a tight battle for the Leading Open Jumper title in the Devon Horse Show.

Dobbs, of Sussex, N.J., won the $7,500 North American League Open Jumper afternoon class yesterday on Marengo, with Laura Chapot of Neshanic Station, N.J., second on Redford. Ward, of Bedford, N.Y., was third on Pandoer in a class that went from 13 starters to three. The scratches were due to a late-afternoon storm that extended the show until tomorrow.

Dobbs' victory gave her a two-point edge over Ward.

Then, in the first class of the evening session, Ward, riding XM, finished first, with Dobbs second on Marengo and Chapot third on Chili Pepper. That put Ward up by two points going into tonight's bonus-point $50,000 Idle Dice Stake.

Dobbs was the Leading Rider last year in her first year in the Open Jumper division. Ward is a two-time Olympic equestrian team gold medalist, six-time Devon Grand Prix champion, and once-each Devon Leading Rider and Champion. Both want that title badly.

For spectators, the good news from yesterday's rain is that four Amateur Owner classes have been moved to tomorrow, starting at 8 a.m., and the Country Fair will be open from 10 a.m. to 2 p.m.

So Devon fans will get one more day to enjoy both the championship competition and the country fair.

Heavy rain early yesterday morning made the Dixon Oval look more like a shallow lake than a competition arena, so in the interest of safety for both horse and rider, most of the day's classes were either canceled or postponed.

But with tractors and squeegees working from 7 a.m. on, the ring became usable by 5 p.m., allowing two of the jumper classes scheduled for the day to be completed, and the evening schedule, which began after the last of the storms had passed, ran pretty much as scheduled.

Erika Pritz of Chicago won the Amateur Owner Jumper, Time First Jump-Off, on her Landessa, in a time of 40.089. Caroline Curcio of West Islip, N.Y., with the only other clean round in the jump-off, finished second in 43.950.

The evening Coaching competition was canceled, and the championship, awarded on the basis of points won through the first four days, went to Mr. and Mrs. Harvey Waller's Road Coach, with Harvey Waller of Stockbridge, Mass., as whip. The four-in-hand accumulated 13 points.

It was the Wallers' fourth consecutive championship at Devon, and their fifth in six years.

Tied for Reserve champion with 11 points were the four-in-hand of George A. Weymouth of Chadds Ford, with Robert Longstaff as whip, and the Road Coach owned by James and Misdee Wrigley of Lakewood Ranch, Fla., with Misdee Wrigley the whip.