Jack Silkma made two free throws with two seconds to play tonight to enable the Seattle SuperSonics to hold off the Phoenix Suns, 114-110, and capture the National Basketball Association's Western Conference championship for the second year in a row.

Phoenix, which trailed 112-104 with less than a minute to play Paul Westphal intentionally missed a free-throw attempt in hopes bounded and was fouled.

Seattle will meet the winner of Friday's Eastern Conference championship game between Washington or San Antonio in a best-of-seven championship series beginning Sunday of the Eastern champion's home court.

Sikma scored a career high of 33 points, Gus Williams added 29 and Dennis Johnson had 26 for the Sonics, who won before a Kingdome crowd of 37,552, largest in the NBA this season and second largest in the league's playoff history.

The Sonics led by 15, 100-85, with six minutes to play, but the Suns never quit. By pressing and scrapping to the very end, they cut the lead to 112-110 with two quick steals in the final 12 seconds and had Westphal at the foul line to shoot one shot.

Westphal purposely missed the free throw. It bounced off the back rim to Sikma, who was fouled by Don Buse. Sikma made both free throws to ice the victory.

The Suns started Alvan Adams at center in an attempt to catch the Sonics by surprise. Adams sprained his ankle in the third game of the series and hadn't played since. He scored the Suns' first basket tonight on a 10-foot jump shot, but Seattle's Gus Williams hit two quick 20-foot jumpers to get his team an early 6-4 advantage.

Three straight points by Admas later in the period gave the Suns a 20-16 lead, but again Williams got the Sonics going. First he hit a 15-footer after a bad adams pass and then intercepted Adams' ensuing inbounds pass and scored on a drive to tie it at 20-20 with 5:20 left in the quarter.

Gar Heard scored four points and Mike Bratz two to bring the Suns back from a 26-23 deficit later in the quarter to a 29-26 lead. They held on to lead by a point, 29-28, at the end of the period.

Williams had eight points in the quarter and his running mate at guard, Dennis Johnson, had nine points and five rebounds. Two of his baskets came after he got offensive rebounds.

The score wast ied four times in the first period and the lead changed four times.

The teams traded free throws in the opening minutes of the second quarter before the Sonics exploded on an 11-2 spurt to turn a 30-29 deficit into a 40-32 lead with 7:49 left in the half.

Williams started the Seattle string with a fast-break layup after taking a pass from Fred Brown. Lonnie Shelton made a free throw and Ted McClain scored the Suns' only basket in that 2 1/2-minute span on a drive.

The Sonics answered with eight straight points, four by reserve Wally Walker. Williams hit another 20-footer and Paul Silas tapped in a Brown miss.

When the Suns called time to regroup, Coach John MacLeod obviously told them to go to Paul Westphal. Westphal, held to just two free throws to that point, scored 13 points in the last 7:39 of the quarter to get the Suns within four points, 57-53, at the half.

Westphal scored the Suns' last six points. Two came on an incredible left-handed scoop shot after the Sonics turned the ball over against the Phoenix press.

With the press and their running game working, the Suns negated some of Seattle's strength inside and pulled themselves back into the game. All but two of Westphal's second-quarter points came in transition or off fast breaks.

The Suns scored six straight points early in the third period to tie the score once again at 61. Adams had the last four points in the spurt.

The score was tied five times in the next six minutes. Phoenix never led in that span and Seattle never led by more than two points until Dennis Johnson made a 17-footer (giving him 10 points in the period) and Paul Silas scored on a left-handed turnaround jumper.

The Sonics also scored the last five points of the quarter-three were by Sikma, giving him 22 to that point--and took an 82-75 lead into the game's final 12 minutes.

Phoenix scored the first four points of the fourth period to cut the margin to three, but Williams scored five straight to get the Seattle lead up to 87-79.