A ROMANTIC WEEKEND for just the two of you sounds terrific, but who's going to take the kids? Grandparents just aren't what they used to be. For one thing, they tend to live in Ohio or California, or some other out-of-the-way place; for another, they're probably going skiing or snorkeling this weekend themselves.

Many parents rely on I'll-take-your-darlings-if-you'll-take- mine, which works best if you have friends with kids of similar age and/or temperament, and some extra space to stuff them in. (Forget about The Jewel -- the sitter whose name and number even your best friend won't tell you.)

There are other methods of obtaining sitters, of course. You can, for example, raise your own, or start cultivating friendships with neighborhood kids when they're eight or nine.

If you haven't planned quite that far ahead, you can use a babysitting service, probably the most expensive but oh-so-reliable method. For about $6 per hour, or $60 per day, you can hire a mature woman or man whose background has been carefully checked, a person who makes her entire living lavishing attention on children.

Places like Mothers-in-Deed and Sitters Unlimited check from three to six references, try the sitters out on small jobs, and look for someone with "basic common sense who could cope in an emergency," says Bonnie Gillespie of Mothers-in- Deed.

Some, like Sitters Unlimited, take on children with special needs (and the elderly) if there's no nursing involved, but many are reluctant to take on families with teens ("Who's going to enforce the rules of the house?" asks one owner of a sitting service.).

In most agencies, either the manager or the potential sitter will make a home visit before a big commitment like a weekend, and run through the routine with the parents. "We need to know things like where they can ride their bikes, who needs a bath, when they have to do their homework -- things kids tend to tell you differently," says Nancy Richards of Sitters Unlimited. "And the kids need to be told who will implement the family routine once the parents leave."

The services also make sure the sitter has all the emergency information about the house -- where the fuse box is, how to turn off the water and lock all the doors -- plus a list of phone numbers for neighbors, doctors, transportation and medical releases. "We get cases where the people call every day to check on their pet, and others where they don't phone at all for two weeks," says Richards, "so we need to get all these things nailed down."

You can probably get a slightly better rate if you're willing to ferret out a sitter yourself, and do a little checking and training. One good place to start is your nearest college or university: Most maintain a bulletin board in the student center where you can advertise for sitters, and some even have a list of people interested in taking such jobs. Typically, college students are looking for a long-term commitment -- anything from a regular Saturday afternoon job, to free room and board in exchange for sitting,

People who need a sitter for a weekend tend to need sitters for other times, too, and trying a student out for a few evenings should provide a good feel for whether it would work for a weekend. One fellow we know used that approach to get a sitter who not only cared for his son for the weekend, but, for an extra fee, also helped paint the living room.

Which brings us to an important point about sitting: These people are coming to care for your children, not clean your house. While most of them are willing to either do dishes or supervise clean-up, and, for long-term sits, possibly do a load of laundry or run to the store for milk, they are really there to make your children, not your house, sparkle.

Here's how to find the child-sparklers: PROFESSIONAL BABYSITTING SERVICES

The Yellow Pages are full of these, listed under Sitters. Those that include nursing services tend to be more expensive, and possibly more professional than you need. Here are three with good track records on straightforward child care:

MOTHERS-IN-DEED -- 3219 Columbia Pike, Suite 306, Arlington, VA 22204, 920-2454. Fifteen years in the business. Charges $60 per calendar day, plus a $35 fee to the agency, for one to seven days. Checks three work references plus work history for past five years. Prefers to start sitter at a time when parent is in the home, and work up to overnights. Sitter interviews with parents, and parents are given list of other clients.

MOTHERS' AIDES -- 10911, Carters Oak Way, Burke, VA 22015. 250-5622. Seven years in the business. Charges $60 per 24 hours for one child, plus $5 each additional child, and $3.50 transportation fee. Checks four to six work and personal references. Hires "educated" widows, grandmothers and nurses. Need two weeks' notice.

SITTERS UNLIMITED -- 205 Yokum Parkway, Alexandria, VA 22304, 823- 0888. Part of a national franchise running out of San Diego, Sitters Unlimited has been in the area three years. Charges $60 per day for first child, $10 for each additional child. Owner of service conducts home visit, which includes a packet of forms to complete (medical and transportation releases, etc.). Checks minimum of two professional references, asks for more. Provides care for special needs and the elderly, provided there's no nursing involved. Needs "several weeks warning" for overnight sits. COLLEGE STUDENT SITTERS

Most schools are willing to at least post notices for babysitting. Here's a brief sampling:

AMERICAN UNIVERSITY -- Career Center, 4400 Massachusetts Avenue NW, Washington DC 20016. 885-1800. For the cost of reproduction, will send a list of potential sitters. Also has part-time job board where you can post a notice.

GEORGE WASHINGTON UNIVERSITY -- Career Services Center, 801 22nd Street NW, Suite T509, Washington DC 20052. 676-6496. Maintains a full- part-time job listing, and will post notices for babysitters. Most of the students, however, are looking for jobs on a long-term basis.

UNIVERSITY OF MARYLAND -- Stamp Union, Information Desk, College Park, MD 20742. 454-2801. If you mail in your notice, they'll put it up if there's room. They recommend bringing in the notice yourself and checking with them first.

NORTHERN VIRGINIA COMMUNITY COLLEGE ALEXANDRIA CAMPUS -- 845-6207. Student Activities will post a notice if you phone in.

ANNANDALE CAMPUS -- 8333 Little River Turnpike, Annandale, VA 22003. 323-3147. If you mail your notice, they'll post it in the Student Activities Office.