In Philadelphia this weekend and next, you can steal a march on spring -- and on summer, too, for that matter -- at the 1983 Philadelphia Flower Show, which will offer everything from summery flower-strewn sailboats in a marina to an ice-skating scene in a snow-covered cedar swamp about to burst into spring bloom.

"The contrast between the plants of mid-summer and those of early spring will be quite spectacular," says Jane G. Pepper, a native of Scotland, who since 1980 has been executive director of the Philadelphia Horticultural Society, the show's producer.

No ordinary flower show, this annual extravaganza has been a Philadelphia tradition since 1829 and rivals the famous Mummers' New Year's Day Parade as the city's most colorful and fanciful annual event.

This year's show will cover five acres in the Civic Center (34th Street and Civic Center Boulevard) with 173 major exhibits and 1,500 individual entries in 163 competitive classes. There'll be a mid-Victorian Brighton pavilion and a display of 3,000 orchids in myriad colors and varieties.

On the theme of "Follow the Sun," Winterthur and other prominent gardens of the Delaware Valley will sponsor major exhibits, as will area florists, landscape nurseries and university horticulture departments.

But flowers aren't all Philadelphia has to offer the weekend visitor. No longer a vaudeville joke, the city abounds with sights to see and things to do.

Philadelphia's renaissance began in the '50s with what has come to be regarded as a model urban-renewal and restoration program. Long known for its historic buildings, art collections, museums, universities, world-class orchestra and baseball team, the city now has a vibrant downtown area that boasts some of the best restaurants in the country and dozens of sophisticated shops.

W. C. Fields, if he were to return today, would hardly be prompted to repeat his much-quoted line: "I went to Philadelphia oe Sunday and it was closed." SEEING THE SIGHTS

For newcomers, sightseeing in Philadelphia should begin with Independence Hall and the Liberty Bell, in INDEPENDENCE NATIONAL HISTORICAL PARK. Stop at the Visitors' Center (Third and Chestnut streets) for information about tours and other national landmarks in this most historic square-mile in the country.

Here the First Continental Congress met in Carpenters' Hall. At Graff House, Thomas Jefferson wrote the Declaration of Independence. The Liberty Bell summoned citizens to Independence Square on July 8, 1776, to hear the document read publicly for the first time. Independence Hall housed the Second Continental Congress and the Constitutional Convention presided over by George Washington. Franklin Court, the site of Benjamin Franklin's home, includes an underground museum that shouldn't be missed.

Library Hall contains an unsurpassed collection of Franklin's books and papers and the library of the American Philosophical Society. The list goes on to include the First and Second Banks of the United States, the Philadelphia Exchange, Congress Hall and the Old City Hall, first home of the Supreme Court.

Nearby you'll find CHRIST CHURCH (Second and Market streets), where Washington, Jefferson, Franklin and Betsy Ross worshipped and where seven signers of the Declaration of Independence are buried. A block away is the BETSY ROSS HOUSE (239 Arch Street). A few steps farther is the cobblestoned ELFRETH'S ALLEY (between Arch and Race, Front and Second streets), lined with houses dating back to the early 1700s and claiming to be the oldest continuously occupied residential street in America.

In the same area of the city are the PHILADELPHIA MARITIME MUSEUM (321 Chestnut Street), which traces the maritime history of the natioin and the region, and the largest U.S. MINT (Fourth and Arch streets).

One of the most historically significant warships preserved from America's past, the U.S.S. Olympia, is berthed at PENN'S LANDING (between Market and Lombard streets) on the Delaware River. She was Commodore George Dewey's flagship at Manila Bay. Other attractions in the waterfront park include the Portuguese Trail Ship Gazela Primiero; the WWII guppy-class submarine, U.S.S. Becuna; and the largest steel sailing ship still afloat, the Moshulu, now a museum and floating restaurant.

A stroll past the restored Georgian and Federal town-houses of SOCIETY HILL, named for the Society of Free Traders to whom Penn granted a tract of land west of his landing, could take you to the PENN MUTUAL BUILDING (510 Walnut Street). Here you can visit the observation deck for a panoramic view of Philadelphia, Tuesday through Saturday; but you'll have to do this by March 12, after which it will be closed to the public. En route, stop at the SAMUEL POWEL HOUSE (244 South Third Street) where he and Mrs. Powel entertained elegantly. An entry in John Adams' diary notes "... a most sinfull feast again! Every thing which could delight the eye or allure the taste." Sally Franklin wrote to her father in London that she had danced with President Washington in the great second-floor ballroom.

In the center of the city and dominating its skyline is CITY HALL (Broad and Market streets), a Victorian structure crowned by a 37-foot bronze statute of William Penn done by Alexander Milne Calder in 1894. Some works by his son are on view at CENTRE SQUARE (1500 Market Street), PENN CENTER PLAZA (17th and JFK Boulevard) and other locations, as part of the city's innovative public art program. Class Oldenburg's famous "Clothespin" also is at Centre Square, and the work of other well-known contemporary arists can be seen throughout the downtown area.

The PENNSYLVANIA ACADEMY OF FINE ARTS (Broad and Cherry streets) houses, in a beautifully restored Victorian building, one of the country's finest collections of early American paintings. From here, it's but a few blocks to the Benjamin Franklin Parkway.

The Parkway, where visitors can watch Philadelphia's St. Patrick's Day parade on March 13, leads from John F. Kennedy Plaza past Logan Circle to the East and West River drives of Fairmount Park. Near the entrance to the Park, you'll pass the ACADEMY OF NATURAL SCIENCES, the FRANKLIN INSTITUTE, the RODIN MUSEUM and the PHILADELPHIA MUSEUM OF ART, each of which deserves an extended visit.

Within the park's boundaries along both sides of the Schuylkill River, are 18th-century country houses open to the public. Robert Morris, signer of the Declaration of Independence, once owned the land where LEMON HILL now stands, the favorite of many visitors; the present Palladian house built by John Pratt in 1799 and 1800 stood in a grove of lemon trees.

MOUNT PLEASANT, a graceful Georgian structure, was built by a Scottish privateer and later purchased but never occupied by Benedict Arnold. Its ornate woodwork and Chippendale furnishings alone are well worth a visit. John C. Calhoun, he Marquis de Lafayette and Daniel Webster were entertained at STRAWBERRY MANSION when it was called "Summerville." The largest house in the park, it acquired its present name in the mid-19th century when it was a dairy farm serving strawberries grown from roots imported from Chile. WOODFORD is a charming example of colonial architecture. Completely furnished as an 18th-century home, the mansion almost makes you believe that Benjamin Franklin, a frequent visitor, has just stepped from the parlor. The PHILADELPHIA ZOOLOGICAL GARDEN, the nation's first, lies within the park.

If the sun has followed you here from the flower show, you may want to stroll along the park's East River Drive, enjoying the hints of spring and imagining you are seeing Thomas Eakins' scullers on the Schuylkill.

If, instead, you're up to more sightseeing, there's the EDGAR ALLAN POE HOUSE (532 North Seventh Street) or the NORMAN ROCKWELL MUSEUM in the Curtis Building (Sixth and Walnut streets). You might like to see the rare books and manuscripts at the ROSENBACH MUSEUM & LIBRARY (2010 Delancey Place) or visit the AFRO-AMERICAN HISTORICAL & CULTURAL MUSEUM (Seventh and Arch streets).

Philadelphia's ACADEMY OF MUSIC (Broad and Locust streets) is the oldest concert hall and opera house in the country. Unless you're attending a performance, the home of the Philadelphia Orchestra, now under the baton of Riccardo Muti, can be admired only from the outside, except for the second Tuesday of each month when its doors open to visitors for tours.

The UNIVERSITY OF PENNSYLVANIA'S MUSEUM (33rd and Spruce streets), near the Civic Center, is noted for its archaeological and anthropological collections. And there's the MUMMERS MUSEUM (Second street and Washington avenue), where the fantastic finery of parades past is on display.

Described as a "walker's paradise" by John Francis Marion, Philadelphia and its historical sites can easily be explored on foot.Marion's book, Bicentennial City, is an extraordinary guide. Although out of print, it may be found in libraries and second-hand bookstores. SPENDING MORE THAN TIME

Shopping in Philadelphia may begin at John Wanamaker's (13th and Market streets) but it doesn't end there. The Gallery (Ninth and Market streets), an enclosed mall under a glass roof, has 125 shops and restaurants including Strawbridge & Clothier and Gimbels.

The Bourse (Independence Mall East between Fourth and Fifth streets), Philadelphia's old commodities market, now houses three tiers of sophisticated boutiques, stores and restaurants around a central courtyard.

NewMarket, near Society Hill's Head House Square (Second and Pine streets) in what was the old Swedish section of town, is the newest shopping complex. The glass-and-aluminum structure contrasts stunningly with the old brick of the earlier buildings. A block away is South Street, noted for its arts and crafts galleries.

The antique shops along Pine Street and Jewelers Square on Sansom Street are worth exploring, but the Italian Market (Ninth and Christian streets) is probably the most fun. It bustles with noise, color and aroma especially on Fridays and Saturdays, and some of the best hoagies can be found here; just don't call them heroes. FEEDING MORE THAN YOUR SPIRIT

Other culinary delights abound in the city; more than 375 new restaurants have opened in the past five years. Among the best are Le Bec Fin (1312 Spruce Street), whose chef offers a prix fixe dinner that's expensive but worth it, and the Frog (1524 Locust St.), which lists moderate to expensive choices on its eclectic menu.

Bookbinder's is the famous old Philadelphia name in restaurants, and since the '40s, there have been two: Bookbinder's Seafood House (215 South 15th Street) and Old Original Bookbinder's (125 Walnut Street). They serve excellent seafood and, of course, the traditional snapper soup.

Other restaurants in the Center City area include Friday Saturday Sunday (261 South 21st Street), an attractive neighborhood restaurant near Rittenhouse Square, which serves well-prepared American and continental cuisine. The Garden (1617 Spruce Street), in a brownstone that once was a music academy, is especially popular for lunch and serves American food with a Gallic touch. The Commissary (1710 Sansom Street) has an inexpensive gourmet cafeteria downstairs and a full-service restaurant upstairs where prices are higher. Near the Civic Center is La Terrasse (3432 Sansom Street) on the University of Pennsylvania campus. Its French cuisine is moderately priced.

The City Tavern (Second and Walnut streets), frequented by Jefferson. Washington, Franklin and other leaders in the revolt against George III, is one of the sites of Independence National Historic Park. Costumed waiters serve early-American fare.

The Dickens Inn at NewMarket (Second and Pine streets) is owned by a descendant of Charles Dickens.This English pub has a fantastic bakery. Another popular NewMarket restaurant is Cafe Lisboa specializing in Portuguese cuisine. A favorite northern Italian restaurant nearby is La Famiglia (8 Front Street). GETTING THERE & STAYING THERE

Most Philadelphia hotels, including the finest, have special packages for weekend visitors. Rates per-person, double occupancy for two nights, Friday or Saturday arrival, with two full American breakfasts and a half-day motorcoach tour are $107 at the recently renovated Bellevue Stratford (Broad and Walnut streets), $103 at the elegant old Barclay Hotel (18th and Rittenhouse Square), $86 at the deluxe Warwick (17th and Locust streets), $79 at the Hilton Hotel (18th and Market streets) and $62 at the Penn Center Inn (20th and Market streets).

At the small SOCIETY HILL HOTEL (301 Chestnut Street) overlooking Independence National Historical Park, the rate is $75 per person for two nights, including continental breakfasts. BED AND BREAKEAST OF PHILADELPHIA will provide you with information on rooms that rent for reasonable rates in private homes, guest homes, inns and small hotels. Call 215/884-1084 or write P.O. Box 101, Oreland. PA 19075.

Getting to Philadelphia is easy: AMTRAK, with an excursion fare of $35 roundtrip if you don't travel between 1 and 7 p.m., can get you there in two hours. The regular roundtrip fare is $50 for the train that delivers you to 30th Street Station, convenient to the Flower Show, Driving the 140 miles will take somewhat longer and flying is considerably more expensive. Prices range from EASTERN $160 to RANSOME'S $98 for a roundtrip ticket.

Once you're there, getting around is even easier. SEPTA's bus and subway service will take you most places you want to go for 75 cents. The town-and-country tour on the FAIRMOUNT PARK TROLLEY costs $4.50 and leaves daily at 1 from the Tourist Center (16th street and JFK Boulevard). The trolley travels through Independence National Historical Park, Society Hill and Fairmount Park.

More information about Philadelphia's tourist attractions, shops, restaurants and nightlife can be obtained from the CONVENTION AND VISITORS BUREAU/TOURIST CENTER, 215/568-6599. The PHILLY FUN PHONE'S number is 215/568-7255: the caller receives a taped listing of special events, updated every 24 hours. Information about the Flower Show (general admission is $5.50) can be obtained from the PHILADELPHIA HORTICULTURAL SOCIETY, 215/625-8260.