Trans World Airlines Inc. said yesterday that it has reached a tentative agreement with the Air Line Pilots Association under which the pilots would make pay and work-rule concessions worth about $100 million in 1986.

The pilots union in Washington had no comment.

Meanwhile, Eastern Airlines yesterday asked its 4,200 pilots to take more pay cuts in 1986 and to adopt a two-tier wage scale under which new pilots would receive lower salaries, the pilots union said.

The TWA agreement must be approved by a council of 18 TWA pilots and by Carl Icahn, the New York investor who acquired 51 percent of TWA's stock after a hotly contested takeover battle.

Harry A. Hoglander, the TWA pilots' chief, said the tentative agreement calls for TWA's pilots to take pay cuts and make work-rule changes that together would save TWA 26 percent on pilot costs. The agreement is in accord with a pact the pilots union reached last August with Icahn, he said.

In that agreement, the pilots pledged to take a 26 percent pay cut in return for a share of TWA's profits and equity if Icahn won the airline.

The tentative agreement comes as Icahn apparently is attempting to alter the terms of his purchase of TWA's remaining stock.

Icahn is trying to lower the cash portion of his offer for TWA's shares, partly because the airline business has deteriorated since last summer when he offered to pay $19.50 in cash and $4.50 in preferred stock for the roughly 17 million TWA shares he doesn't own. Sources say Icahn now wants to pay $15 or less in cash. Since Icahn made his agreement with TWA in September, TWA has announced a loss of $13.5 million in its normally healthy third quarter.

In Miami, Eastern officials said yesterday they would not comment on the proposal to their pilots because the company hopes to negotiate in private with the Air Line Pilots Association.

"Our costs are totally out of whack with the way the industry is going," Eastern spokesman Jerry Cosley said. "We are looking for long-term, more meaningful reductions." He admitted that one possibility is a two-tier wage structure under which Eastern could hire new pilots at a lower wage scale than its current staff.

Eastern Chairman Frank Borman said in recent interviews that, although Eastern made a profit of $78 million during the first nine months of the year, he could not say whether there will be any profit left at the end of the year. He said fourth-quarter fare-cutting started by low-cost carriers such as People Express could erode the rest of the year's earnings.