A 72-hour dance marathon to benefit the American Cancer Society, sponsored by Phi Sigma Delta fraternity of University of Maryland, begins at 8 o'clock tonight at Ritchie Coleseum.

The dancing - disco, jitterbug and many other varieties - is to continue through 8 p.m. Sunday. Sponsors say all proceeds, after expenses, will go to the Cancer Society. Expenses usually run from $5,000 to $7,000, sponsors say. This is the eighth dance marathon to be held by the Phi Sigma Delta. Last year's event raised $52,000 for the American Cancer Society.

The public is invited to watch the dancing, and there is no admission charge. Ritchie Coloseum is not Rte. 1 in College Park, across from the University of Maryland.

A new edition of the Senior Citizen Directory of Services has been published by the Prince George's County Department of Aging. The 48-page booklet contains information on available housing, transportation, health services, financial aid and leisure and educational activities.

Elderly people who did not receive a copy of the directory in the mail can get one at any branch library, nutrition center, the Red Cross headquarters office in Hyattsville or at any of the 13 senior activity centers in the county. To find the nearest location, call Shirley Wyvill at 350-6666, ext. 362.

Many volunteer opportunities are now available through the Montgomery County Volunteer Bureau. For information, call 729-1666.

As part of a continuing program of cooperative purchasing and servicing arrangements with other jurisdictions, the Price George's County government has signed an agreement with the Town of Forest Heights to maintain and repair their town vehicles. "These cooperative efforts between county government and the 28 municipalities to to pool their resources in such matters have resulted in cost savings of tens of thousands of dollars for all parties," according to Chief Administrative Officer Robert Wilson.

Area optometrists and ophthalmologists have offered their services to the Free Clinic of Rockville Inc. and will be providing glaucoma screening for people over 30 years old on a once a month, appointment basis. The testing for glaucoma, a leading cause of blindness, is free, painless and takes only a few minutes. For information or appointments, call Mark Langlais at 340-9666.

Physicians at Johns Hopkins Medica Institutions in Baltimore are looking for mothers of children with cleft lip to volunteer for a study that could help find the cause of the birth defect. The study's director, Dr. Jennifer R. Niebyl, is interested in gaining the cooperation of women who have a child with cleft lip, nor does the child's father.

Volunteers should either be very early in another pregnancy (no more than three months) or be planning an another pregnancy soon. They must be willing to supply blood and urine samples from one to three times. Volunteers will be paid, and a researcher will come to their homes if they cannot come to Hopkins and live within 100 miles of the city. For information, call Laura Rocco, collect, at 301-955-8673.

Oxon Hill Farm's newest female calf is without a name, so the National Park Service wants your suggestions. Send names to Oxon Hill Farm c/o National Capital Parks-East, 5210 Indian Head Hwy., Oxon Hill. Md. 20021, on a postcard with your name, address and telephone number. Entries must be postmarked by tomorrow. The person who suggests the winning name will be invited to serve as honorary grand farmer at the Oxon Hill Farm Fall Festival, Saturday, Oct. 28, from 10 a.m. to 5 p.m.

Snow tires equipped with studs meeting state design standards may be used now through April 15, the Motor Vehicle Administration has announced. The standards allow up to 150 studs per tire. They may protude no more than 1/16th of an inch from the tire's surface. Except for emergency vehicles and school buses, studed tires are prohibited on vehicles weighing more than 10,000 pounds registered gross weight. During a snow emergency snow tires are required for vehicles traveling on state highways designated as snow emergency routes. Violators may be fined up to $500.