Federal examiners seized control of the still-solvent Lincoln Savings and Loan Association, a large thrift in Irvine, Calif., whose corporate parent contributed heavily to Senate campaigns and had allegedly received favorable treatment from regulators.

The Federal Home Loan Bank Board said the 29-branch S&L had dissipated its assets and was operating in an unsafe and unsound manner. Lincoln, with $5.4 billion in assets, has only about $20 million in capital remaining.Lincoln, the 42nd largest thrift in the nation at the end of 1988, is the second big S&L to be taken over by the government recently even though technically solvent. Gibraltar Savings of Beverly Hills, Calif., was seized March 31.

Regulators stressed that Lincoln's branches would remain open as usual and that all deposits were guaranteed up to the $100,000 insurance limit.

The institution has been up for sale while its parent, American Continental Corp., a luxury resort developer based in Phoenix, Ariz., prepared to file for federal bankruptcy protection, which was done Thursday.

The bank board said Lincoln's financial troubles started in February 1984, when it was bought by American Continental and its management invested in risky real estate ventures, stocks and junk bonds.

"Management appeared to operate Lincoln mainly for the benefit of American Continental Corp. . . . (and) has repeatedly violated regulations . . . and has refused to follow supervisory directives," a bank board statement said.