At Lake Arrowhead, a Lineup of Summer Highlights : Mountain resort offers lodging discounts. More bargains in Monterey.

The mountain community of Lake Arrowhead, nestled 5,500 feet up in the San Bernardino Mountains, is offering a series of senior discounts for lodging and various sightseeing and activity programs in the area. Among the highlights:

* Elderhostel educational travel programs are offered at the Lake Arrowhead Resort (formerly the Lake Arrowhead Hilton), where a six-day learning program includes three days of classes, room accommodations, all meals and use of the hotel’s extensive recreational facilities for $355 per person. Courses are held at various times throughout the summer, and include subjects such as “Physical Fitness Training,” “Cuisine for the Novice or Closet Gourmet” and “Lake Arrowhead History.” Participants must be 60 years of age or older; minimum age for a companion is 50. Elderhostel information is available at College of the Desert, Community Services Department, 43-500 Monterey Ave., Palm Desert 92260, (619) 773-2544.

* The Lake Arrowhead Resort offers “SuperSaver” rates that provide 50% discounts off weekday room rates, and 25% off Saturday. Weekday rates for seniors from now through Sept. 13 are $79.50 per room per night, and $119 on Saturday (the regular rate is $159 per night, weekdays and weekends). From Sept. 14 to Jan. 3, 1994, rates are further reduced to $74.50 weekdays and $109 Saturday (regular rate for this time of year: $149). For reservations and information, call (800) 800-6792.

Other discounts for seniors at Lake Arrowhead Village include:

* 10% off the price of a two-hour ecology exploration walk of nature trails; seniors pay $18. (909) 337-5080.

* $1 off the regular $9.50 fare for a one-hour Lake Arrowhead cruise on the Arrowhead Queen paddlewheeler. (909) 336-6992.

* $1 off the regular $3.50 entrance fee at the Children’s Museum. (909) 336-3093.

Lake Arrowhead Village hosts special weekend events throughout the year, including summer concerts and other programs. For a recorded report of current activities, call the Village Hotline at (909) 336-3274. For brochures on various attractions, write to the Lake Arrowhead Chamber of Commerce, P.O. Box 155, Lake Arrowhead 92352.

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Several hotels in the Monterey area are offering senior discounts that will continue through year’s end.

* The Doubletree Hotel Monterey has a “Silver Leaf” program that provides 20% off nightly room rates year-round to members of AARP or anyone over the age of 55. Rates are reduced to $116 double occupancy and $100 single, down from $145 and $125. For reservations, call (800) 528-0444.

* The Monterey Hotel, Mariposa Motor Inn and Waystation Inn are offering a “Seasoned Travelers” special, Sundays through Thursdays. A two-night stay is required for the per-night room rate of $55. Call the Monterey, (800) 727-0960; the Mariposa, (800) 824-2295, or the Waystation, (800) 858-0822.