Astor United Cruises: Free air fare for passengers departing Oct. 30, Nov. 20 , Dec. 1, and 11.
Bahama Cruise Line: Tampa departures from Oct. 16 to Jan. 15 are $495 (inside cabin) and $575 (outside). Air fare ''add-on'' costs are greatly reduced; Cruise 'n Dive snorkeling program will also cost less.
Carnival Cruise Line: Free air through Jan. 30, 1984, for the Caribbean only (this does not include the Tropicale).
Costa Cruises: 50 percent discount for the second person on the Amerikanis; Free air fare through Dec. 11 for passengers paying top rates on World Renaissance.
Cunard Line: QE2 transatlantic passengers get free British Airways transportation in the other direction; free air fare to San Juan is offered to Cruise 'n Stay passengers.
Delta Queen Steamboat Company: the Steamboatin' Standby fare is $95 per person, per night; there is a 10 percent reduction for early deposit.
Home Lines: Rebates of up to $400 per cabin on fall departures of the Atlantic from Port Everglades; rebates of $300 on Dec. 5 and 12 sailings of Oceanic; free air for both programs.
Norwegian American Cruises: Free air fare for Sagafjord's trans-Panama Canal cruises, plus $250 to $1,000 incentive deductions; the Cruising-Plus concept (in which all expenses - air fare, overnight stay in a hotel, and so on - are included in one price) begins in 1983.
Norwegian Caribbean Lines: Free air fare through Jan. 15, 1984 (except holidays), for seven-day sailings.
Paquet French Cruises: Free air fare from Nov. 28 through May 7 for Rhapsody from most cities; free air fare for Mermoz sailings from San Juan.
Princess Cruises: $250-per-person discounts on Mexico cruises Oct. 30, Nov. 20, 27, and 29, and Dec. 5, plus free air fare; $1,000-per-couple discount on Dec. 11 and Dec. 29 trans-Panama Canal sailings and free air fare. Third person in cabin free.
Royal Caribbean Cruise Lines: Free air fare through 1983 for all cruises, except inaugural month of Song of America; free shore excursions for children.
Royal Viking Line: $750 to $1,500 saving certificates only for passengers booking 12-day or longer cruises before Dec. 12.
Scandinavian World Cruises: Substantial discounts for entire inaugural season; one-way free through January 1983; no charge for cars; third and fourth cabin occupant only $45 each through May.
Sitmar Cruises: Free air for all sailings.
All rates are per person, double occupancy.