Junior federal executives would get pay raises of $5,900 to $8,800 a year under a proposal made yesterday by the Senior Executive Association to a White House group studying compensation of top civil servants.

The proposal is part of a plan to establish a permanent pay differential between starting pay in the government's high-risk, high-reward Senior Executive Service and pay for upper-level career civil servants who are outranked by SES members but sometimes earn more. The association's proposal would raise starting pay in the SES from $64,700 to $73,500.

SES has six pay grades. The regular civil service has 18 general schedule (GS) pay grades.

The association said the increases could become effective if President Reagan would amend an existing executive order that establishes salary levels for the approximately 7,600 SES personnel.

Currently some members of the SES, who trade off some job security for more responsible jobs and the chance for bonuses, are paid less than some longtime civil servants in Grades 15 through 18.

The association, which represents many of the 7,600 SES members, says that some outstanding career employes have refused promotions from the more secure civil service to the fast track SES because doing so would mean a pay cut for them. SES pay ranges from $64,700 to $77,500. About 1,000 association members are in SES level 1, which starts at $64,700, or level 2, which pays $67,600.

About 30,000 career civil servants, including 19,000 here, are in Grade 15 or its equivalent GM (government manager) level. Those at the 10th longevity step of their grade are paid $69,976.

The association made its recommendations for the GS versus SES pay differential at the opening of hearings before the Presidential Commission on Career Federal Executive Compensation. It is chaired by Anne McLaughlin, formerly a top Interior Department official.

Reagan created the executive pay panel this year after announcing pay raises for top career and political appointees. Originally the commission was to make its report in August but because members weren't appointed until June, the deadline for its report has been extended until February.

The commission is expected to recommend substantial pay raises for career government executives whose salaries are now linked to pay increases for members of Congress.Retirement/Insurance

Most federal workers have two important financial decisions to make before the end of this year. For 2 million workers hired before 1984, the choice is the remaining in the current pension plan or moving to a new retirement program. For all government workers and retirees, the decision involves picking an insurance plan to cover them and their families next year, in light of premium increases that average 31 percent.

The retirement choice must be reached by Dec. 31. The health plan open season closes in mid-December.

Tomorrow on WNTR (1050 AM) radio, former Senate staff member Jamie Cowen will talk about the retirement and health insurance situation. Cowen's firm provides computerized pension plan advice to workers, and next month will publish a federal health insurance shopping guide.