Union employes of The Sun and Evening Sun in Baltimore ended a six-day strike yesterday and returned to work after the 700-member Newspaper Guild local agreed to a management contract proposal that many workers said they reluctantly accepted out of fear of losing their jobs.

Guild members returned to their offices wearing "Share The Wealth" buttons and openly discussing what they called an unreasonable pact that required workers for the first time to help pay for health benefits. The contract was approved, they said, only because of the possibility that the papers' owner, Times Mirror Co., would replace workers if the strike continued.

Union negotiator Sandi Polaski said she received a telephone call Tuesday afternoon, after a rally outside the Sun building, in which a "highly placed" Times Mirror employe indicated the company would begin firing people if they didn't accept the contract and return to work.

"The company had been playing such brinkmanship throughout the negotiations I could not disregard the rumor," Polaski said. "If, in fact, Times Mirror was ready for serious strikebreaking, we were in a precarious position."

Management representatives would not answer questions about threats to replace employes. The company said yesterday that it appeared all strikers had returned to work and both papers today would resume full publication.

Members of five other unions at the Sunpapers, who had honored picket lines and refused to work, also returned to their jobs.

The contract was accepted early yesterday by Washington-Baltimore Local 35 of The Newspaper Guild in a 258-to-110 vote after five hours of discussion. After the vote, the membership voted unanimously to ask Times Mirror to fire Publisher Reg Murphy and General Manager Richard M. Basoco, who handled negotiations. Hundreds of the workers then marched to the Sun building on Calvert Street, shouting "Reg Must Go," and threw copies of the contract into the company parking lot.

"It was clear they weren't bargaining and they weren't being reasonable," said Joan Jacobson, a member of the union negotiating committee. "We hate the contract. But we had to be very honest with the membership about what could happen if we did not accept it."

Editorial and commercial workers at the papers struck last week over two provisions they found unacceptable: employe contributions for health benefits and a two-tier wage scale that pays reporters in zoned suburban supplements less than other employes. The Guild accepted a contract with both provisions, although in modified form. The contract requires employes to pay $5.62 per week toward health coverage. It provides raises of 12 percent over three years to reporters and editors and 40 percent for lower-paid suburban employes.

Negotiating team members who urged members to accept the contract said other unions, representing printers, pressmen, engravers, truck drivers and mailers, warned Guild negotiators their membership feared for their jobs and might decide to return to work.

Members from both papers indicated yesterday that union support remained strong despite the aborted strike. "I think people are still really mad," said Michael Wentzel, an Evening Sun reporter. "But nobody's mad at the union. This is my fifth time with negotiations and I have seen people really get angry at the union . . . . This time there's a lot of anger toward the company."