Myra Blackwelder withstood 100-degree temperatures to shoot four-under-par 68 yesterday for a one-stroke lead after the opening round of the $400,000 Dinah Shore tournament at Rancho Mirage, Calif., the first major LPGA event of the year.

Blackwelder, the former Myra Van Hoose and a nonwinner in five years on the tour, gave birth to her first child 10 weeks ago and is playing in only her second tournament since November. But she carded four birdies and no bogeys with a fine display of putting skills and a touch of luck.

Sharing second after a round of the Mission Hills Country Club course were Jane Crafter, Patty Sheehan and Judy Clark . . .

Lesser known than Blackwelder, 5-foot-7, 135-pound Jeff Sluman battled gusty winds for a no-bogey, six-under-par 66 and a one-stroke lead over Sandy Lyle in the first round of the $400,000 Greater Greensboro (N.C.) Open . . .

Kathy Whitworth and Mickey Wright will compete in the eighth annual $500,000 Legends of Golf seniors event at Austin, Tex., April 25-28 and become the first women to compete in a PGA-sanctioned men's tournament. The 28 two-player teams will be competing for $100,000 first prize on a "better ball" basis. The women will be using the same tees as the men.

(LPGA and PGA scores, C7).