The 23rd America's Cup series starts Tuesday. Defending for the United States are Courageous and captain Ted Turner; challenging for Australia are Australia and skipper Noel Robins. The cup is awarded to the country of the boat winning four out of seven races. The Course And The Conditions

A six-leg, 24.3-nautical-mile course will be set up seven miles south-southeast of Brenton Reef Light, near Newport, R. I. The boats may be motionless at times or attain as much as 15 miles an hour, depending on the wind and or the tactical situation. Even a small difference in inherrent boat speed can be significant. A boat faster than its competition by only .03 knot can develop that into a one-minute margin at the finish. Typically, a race should be finished in about four hours. If it is not completed in 51/2 hours it is abandoned.

The series could be run in four consecutive days, theoretically, but it will probably last several weeks because each side is essential to at least two break days and may ask for a third if four races have been completed. The race committee can cancel races if it is too foggy, too windy or too windless - or if a boat or crew is damaged on the way to the starting line. The Boats

The boats are known as "12 meter" because when the waterline length, girth measurements, weight, sail area and other factors are put into one side oa a mathematical formula the product is "12 meters." The formula tends to insure that the boats, while not identical are essentially equal. Each costs about $1.25 million.

Courageous: Sail number US 26. Approximate dimensions: length overall: 67 feet: length on the water line: 45 feet: beam 12 feet: diaplacement: 59.000 pounds: sail area: 1.900 square feet.It was designed by Sparkman and Stephens and successfully defended against Australia's Southern Cross in 1974. Since then it has been modified by Ted Hood to satisfy this year's deck-opening rules, the effect of which is to bring more of the 11-man crew out of the hull and onto the deck.

Australia: Sail number KA 5. Approximate dimensions; length overall; 64.5 feet; length on the waterline 47 feet; beam; 12.3 feet; displacement; 58.000 pounds; sail area; 1.800 square feet. It was designed by Ben Lexcen and Johan Valentijn. Valtentijn worked on Courageous at Sparkman and Stephers. The Skippers

Ted Turner, 38, has won the World Ocean Racing Championship and many other big-boat events. He raced dinghies at Brown University. He captained Mariner in the 1974 trials but lost out to Courageous. He owns the Atlanta Braves baseball team, the Atlantic Hawks basketball team, an Atlanta television station and is the father of five. He works in the family billboard advertising firm.

Turner had a combined 26-9 record against Independence and Enterprise in the defender's trials. He is reported to have put $250,000 of his own money into the syndicate backing the Courageous effort.

Noel Robins, 41, will handle the Australia. He is the 1977 Australian champion in the Olympic-class Soling and an aggressive match-race competitor. An automobile accident at age 20 left him almost totally paralyzed. Expert for a slight limp and a slightly withered arm he is fully recovered. He is a property developer in Perth, his home, and the father of three.

He beat Gretel II, another, Aussie boat, to gain the challenger's finals and then trounced Sverige, the Swedish entry, four straight. Sverige reached the finals by beating France II. Tactics

The Start - The warning gun fires 10 minutes before the start. The boats sail toward each other from opposite ends of the starting line and commence circling, each trying for the tremendous advantage that goes with being over the line first. The main idea in the preliminary maneuvering is to get between the opponent and the starting line and to be ahead as the starting gun sounds. The leeward boat, farthest from the wind, may turn toward the line, hoping to force his opponent over the line early.

Each skipper would like to start at the favoured end of the line. If the starting line, which is an imaginary line between the race committee boat and a buoy some distance away, is exactly perpendicular to the wind neither end is favoured. But if the wind is not perpendicular, the end of the line that makes an acute angle with the wind is favoured because a start there will provide the shortest sailing distance to the windward mark.

The Windward Legs - The boats will be beating as they cross the starting line and they will continue to beat to the windward mark. When beating, both the mainsail and the genoa jib - the leading sail - are pulled in close to the centerline of the boat. If the trailing boat has done poorly at the start it will probably want to get on a tack different from the leader as soon as possible. Unless it is inherently much faster there is little to be gained by following the leader because the leading boat will to some event interfere with the trailing boat's wind as long as they are on the same tack. Once the trailing boat is on a different tack, however, it will have clear air and may profit from the wind direction and the wind shifts. To tack means to turn the boat into the wind far enough to change the sife of the boat over which the wind is blowing.

Since the boats cannot sail more directly into the wind than about 35 degrees, the shifting of the wind in one direction or another means that beating boats must also shift with the wind if they are to maintain the 35-degree angle. If the boats are on different tacks, it is likely that one tack will more directly move a boat toward the windward mark than the other.

That's why the trailing boat wants to be on a tack different from the leader.He hopes that his new course will serve him better than the old. He also hopes that a wind shift will favor him and hurt his opponent. Of course, if a wind shift persists, the adversely affected boat may tack and sail in the more favorable direction.

A constant changing of tacks by the trailing boat and a constant response by the leader is called a tacking duel. The tacks may come every minute or so and a new tack may start as soon as the prior tack is completed - the trailer trying to break away, the leader "covering" to prevent it. If the trailing boat can get out of phase with leader, he will probably gain clearer air and may take the lead.

The Reaching Legs - The wind is behind and somewhat to the side when a boat s reaching. The genoa jib is replaced by a smaller jib and a spinnaker - a parachute-like sail that provides a vast area against which the wind can push. After the boats round the windward mark the first time they are on starboard tack and headed for the jibe mark, which is positioned to the side of the line connecting the windward and leeward marks. Sailing to that mark insures a test of the boat's effectiveness when reaching.

As in beating, the lead boat tries to stay between the mark and the trailing boat. But because the wind is now behind instead of ahead. it cannot maneuver to block the wind from its opponent. Instead, it is the trailing boat which tries to blanket the other, cutting off its wind and hoping to sail past.

The leader may respond by turning to the right somewhat, into the wind. Turning into the wind by both boats will soon carry them well off the direct line between the windward mark and the jibe mark. Eventually, both boats must change course to head more directly toward the jibe mark. The course change often requires the boats to jib.

The Running Leg - When running, the wind is directly behind the boat and pushes against the mainsail and a spinnaker. The run course is theoretically a direct line between the windward and leeward marks. But reaching is somewhat faster than running and the boats may choose to spend part of the leg reaching even though it means an increase in the total distance traveled. The extra speed may more than compensate for the extra distance. The Rules

There are nearly 80 racing rules. They keep the competition orderly and to a certain extent, dictate the tactics. In their most simplified form, the basic rules are these:

A boat must not touch another boat or a mark.

When two opposite-tack boats are on a collision course, the starboard-tack boat has the right-of-way and the port-tack boat must avoid the other.

When two same-tack boats are on a collision course, the leeward boat has the right-of-way and the windward boat must keep clear.

A leeward boat may luff a windward boat.

Except at the starting line, the outside boat must give the inside boat room to round a mark.