Paramount Pictures Chairman Frank Mancuso on Monday condemned as an "escalation" in the 18-week-old writers' strike, a writers' guild interim contract proposed on Friday. Mancuso's statement, made through Alliance of Motion Picture and Television Producers spokesman Herb Steinberg on behalf of the alliance executive committee, said the new proposal was a development from which "the writers and others in the industry might never recover." The proposed interim pact, scheduled to run until May, 1992, would be superseded by any final agreement reached between the guild and the alliance, according to the guild. "We encourage all independent and (alliance) producers to read the (interim) contract, sign it and get the town back to work," responded Brian Walton, chief negotiator for the guild. The guild membership is scheduled to vote on the proposed interim contract on Wednesday.